Rename physfs_platform_macos.c to physfs_platform_apple.m

It's not really "macOS," it's all of Apple's platforms (iOS, watchOS,
tvOS...AppleCarOS? heh), and second...we're about to need access to Cocoa
APIs, so we need it to be Objective-C. I fought as long as I could.  :/

CMakeLists.txt

@@ -26,6 +26,7 @@ include_directories(./src)
 
 if(APPLE)
     set(OTHER_LDFLAGS ${OTHER_LDFLAGS} "-framework CoreFoundation -framework IOKit")
+    set(PHYSFS_M_SRCS src/physfs_platform_apple.m)
 endif()
 
 if(CMAKE_COMPILER_IS_GNUCC)
@@ -38,7 +39,6 @@ if(CMAKE_C_COMPILER_ID STREQUAL "SunPro")
     add_definitions(-xldscope=hidden)
 endif()
 
-
 if(HAIKU)
     # We add this explicitly, since we don't want CMake to think this
     #  is a C++ project unless we're on Haiku.
@@ -73,7 +73,6 @@ set(PHYSFS_SRCS
     src/physfs_unicode.c
     src/physfs_platform_posix.c
     src/physfs_platform_unix.c
-    src/physfs_platform_macos.c
     src/physfs_platform_windows.c
     src/physfs_platform_os2.c
     src/physfs_archiver_dir.c
@@ -89,6 +88,7 @@ set(PHYSFS_SRCS
     src/physfs_archiver_iso9660.c
     src/physfs_archiver_vdf.c
     ${PHYSFS_CPP_SRCS}
+    ${PHYSFS_M_SRCS}
 )