cmake: avoid re-running checks by wrapping check_c_compiler_flag

cmake/sdlcompilers.cmake

@@ -29,13 +29,19 @@ function(sdl_target_compile_option_all_languages TARGET OPTION)
   endif()
 endfunction()
 
+macro(cached_check_c_compiler_flag _arg _var)
+  if(NOT DEFINED "${_var}")
+    check_c_compiler_flag("${_arg}" "${_var}" ${ARGN})
+  endif()
+endmacro()
+
 function(SDL_AddCommonCompilerFlags TARGET)
   option(SDL_WERROR "Enable -Werror" OFF)
 
   get_property(TARGET_TYPE TARGET "${TARGET}" PROPERTY TYPE)
   if(MSVC)
     cmake_push_check_state()
-    check_c_compiler_flag("/W3" COMPILER_SUPPORTS_W3)
+    cached_check_c_compiler_flag("/W3" COMPILER_SUPPORTS_W3)
     if(COMPILER_SUPPORTS_W3)
       target_compile_options(${TARGET} PRIVATE "$<$<COMPILE_LANGUAGE:C,CXX>:/W3>")
     endif()
@@ -47,7 +53,7 @@ function(SDL_AddCommonCompilerFlags TARGET)
       # See if GCC's -gdwarf-4 is supported
       # See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101377 for why this is needed on Windows
       cmake_push_check_state()
-      check_c_compiler_flag("-gdwarf-4" HAVE_GDWARF_4)
+      cached_check_c_compiler_flag("-gdwarf-4" HAVE_GDWARF_4)
       if(HAVE_GDWARF_4)
         target_compile_options(${TARGET} PRIVATE "$<$<OR:$<CONFIG:Debug>,$<CONFIG:RelWithDebInfo>>:-gdwarf-4>")
       endif()
@@ -57,7 +63,7 @@ function(SDL_AddCommonCompilerFlags TARGET)
     # Check for -Wall first, so later things can override pieces of it.
     # Note: clang-cl treats -Wall as -Weverything (which is very loud),
     #       /W3 as -Wall, and /W4 as -Wall -Wextra.  So: /W3 is enough.
-    check_c_compiler_flag(-Wall HAVE_GCC_WALL)
+    cached_check_c_compiler_flag(-Wall HAVE_GCC_WALL)
     if(MSVC_CLANG)
       target_compile_options(${TARGET} PRIVATE "/W3")
     elseif(HAVE_GCC_WALL)
@@ -67,25 +73,25 @@ function(SDL_AddCommonCompilerFlags TARGET)
       endif()
     endif()
 
-    check_c_compiler_flag(-Wundef HAVE_GCC_WUNDEF)
+    cached_check_c_compiler_flag(-Wundef HAVE_GCC_WUNDEF)
     if(HAVE_GCC_WUNDEF)
       sdl_target_compile_option_all_languages(${TARGET} "-Wundef")
     endif()
 
-    check_c_compiler_flag(-Wfloat-conversion HAVE_GCC_WFLOAT_CONVERSION)
+    cached_check_c_compiler_flag(-Wfloat-conversion HAVE_GCC_WFLOAT_CONVERSION)
     if(HAVE_GCC_WFLOAT_CONVERSION)
       sdl_target_compile_option_all_languages(${TARGET} "-Wfloat-conversion")
     endif()
 
-    check_c_compiler_flag(-fno-strict-aliasing HAVE_GCC_NO_STRICT_ALIASING)
+    cached_check_c_compiler_flag(-fno-strict-aliasing HAVE_GCC_NO_STRICT_ALIASING)
     if(HAVE_GCC_NO_STRICT_ALIASING)
       sdl_target_compile_option_all_languages(${TARGET} "-fno-strict-aliasing")
     endif()
 
-    check_c_compiler_flag(-Wdocumentation HAVE_GCC_WDOCUMENTATION)
+    cached_check_c_compiler_flag(-Wdocumentation HAVE_GCC_WDOCUMENTATION)
     if(HAVE_GCC_WDOCUMENTATION)
       if(SDL_WERROR)
-        check_c_compiler_flag(-Werror=documentation HAVE_GCC_WERROR_DOCUMENTATION)
+        cached_check_c_compiler_flag(-Werror=documentation HAVE_GCC_WERROR_DOCUMENTATION)
         if(HAVE_GCC_WERROR_DOCUMENTATION)
           sdl_target_compile_option_all_languages(${TARGET} "-Werror=documentation")
         endif()
@@ -93,10 +99,10 @@ function(SDL_AddCommonCompilerFlags TARGET)
       sdl_target_compile_option_all_languages(${TARGET} "-Wdocumentation")
     endif()
 
-    check_c_compiler_flag(-Wdocumentation-unknown-command HAVE_GCC_WDOCUMENTATION_UNKNOWN_COMMAND)
+    cached_check_c_compiler_flag(-Wdocumentation-unknown-command HAVE_GCC_WDOCUMENTATION_UNKNOWN_COMMAND)
     if(HAVE_GCC_WDOCUMENTATION_UNKNOWN_COMMAND)
       if(SDL_WERROR)
-        check_c_compiler_flag(-Werror=documentation-unknown-command HAVE_GCC_WERROR_DOCUMENTATION_UNKNOWN_COMMAND)
+        cached_check_c_compiler_flag(-Werror=documentation-unknown-command HAVE_GCC_WERROR_DOCUMENTATION_UNKNOWN_COMMAND)
         if(HAVE_GCC_WERROR_DOCUMENTATION_UNKNOWN_COMMAND)
           sdl_target_compile_option_all_languages(${TARGET} "-Werror=documentation-unknown-command")
         endif()
@@ -104,27 +110,27 @@ function(SDL_AddCommonCompilerFlags TARGET)
       sdl_target_compile_option_all_languages(${TARGET} "-Wdocumentation-unknown-command")
     endif()
 
-    check_c_compiler_flag(-fcomment-block-commands=threadsafety HAVE_GCC_COMMENT_BLOCK_COMMANDS)
+    cached_check_c_compiler_flag(-fcomment-block-commands=threadsafety HAVE_GCC_COMMENT_BLOCK_COMMANDS)
     if(HAVE_GCC_COMMENT_BLOCK_COMMANDS)
       sdl_target_compile_option_all_languages(${TARGET} "-fcomment-block-commands=threadsafety")
     else()
-      check_c_compiler_flag(/clang:-fcomment-block-commands=threadsafety HAVE_CLANG_COMMENT_BLOCK_COMMANDS)
+      cached_check_c_compiler_flag(/clang:-fcomment-block-commands=threadsafety HAVE_CLANG_COMMENT_BLOCK_COMMANDS)
       if(HAVE_CLANG_COMMENT_BLOCK_COMMANDS)
         sdl_target_compile_option_all_languages(${TARGET} "/clang:-fcomment-block-commands=threadsafety")
       endif()
     endif()
 
-    check_c_compiler_flag(-Wshadow HAVE_GCC_WSHADOW)
+    cached_check_c_compiler_flag(-Wshadow HAVE_GCC_WSHADOW)
     if(HAVE_GCC_WSHADOW)
       sdl_target_compile_option_all_languages(${TARGET} "-Wshadow")
     endif()
 
-    check_c_compiler_flag(-Wunused-local-typedefs HAVE_GCC_WUNUSED_LOCAL_TYPEDEFS)
+    cached_check_c_compiler_flag(-Wunused-local-typedefs HAVE_GCC_WUNUSED_LOCAL_TYPEDEFS)
     if(HAVE_GCC_WUNUSED_LOCAL_TYPEDEFS)
       sdl_target_compile_option_all_languages(${TARGET} "-Wno-unused-local-typedefs")
     endif()
 
-    check_c_compiler_flag(-Wimplicit-fallthrough HAVE_GCC_WIMPLICIT_FALLTHROUGH)
+    cached_check_c_compiler_flag(-Wimplicit-fallthrough HAVE_GCC_WIMPLICIT_FALLTHROUGH)
     if(HAVE_GCC_WIMPLICIT_FALLTHROUGH)
       sdl_target_compile_option_all_languages(${TARGET} "-Wimplicit-fallthrough")
     endif()
@@ -132,12 +138,12 @@ function(SDL_AddCommonCompilerFlags TARGET)
 
   if(SDL_WERROR)
     if(MSVC)
-      check_c_compiler_flag(/WX HAVE_WX)
+      cached_check_c_compiler_flag(/WX HAVE_WX)
       if(HAVE_WX)
         target_compile_options(${TARGET} PRIVATE "$<$<COMPILE_LANGUAGE:C,CXX>:/WX>")
       endif()
     elseif(USE_GCC OR USE_CLANG OR USE_INTELCC OR USE_QNX)
-      check_c_compiler_flag(-Werror HAVE_WERROR)
+      cached_check_c_compiler_flag(-Werror HAVE_WERROR)
       if(HAVE_WERROR)
         sdl_target_compile_option_all_languages(${TARGET} "-Werror")
       endif()
@@ -152,12 +158,12 @@ function(SDL_AddCommonCompilerFlags TARGET)
   endif()
 
   if(USE_CLANG)
-    check_c_compiler_flag("-fcolor-diagnostics" COMPILER_SUPPORTS_FCOLOR_DIAGNOSTICS)
+    cached_check_c_compiler_flag("-fcolor-diagnostics" COMPILER_SUPPORTS_FCOLOR_DIAGNOSTICS)
     if(COMPILER_SUPPORTS_FCOLOR_DIAGNOSTICS)
       sdl_target_compile_option_all_languages(${TARGET} "-fcolor-diagnostics")
     endif()
   else()
-    check_c_compiler_flag("-fdiagnostics-color=always" COMPILER_SUPPORTS_FDIAGNOSTICS_COLOR_ALWAYS)
+    cached_check_c_compiler_flag("-fdiagnostics-color=always" COMPILER_SUPPORTS_FDIAGNOSTICS_COLOR_ALWAYS)
     if(COMPILER_SUPPORTS_FDIAGNOSTICS_COLOR_ALWAYS)
       sdl_target_compile_option_all_languages(${TARGET} "-fdiagnostics-color=always")
     endif()