Split up CFLAGS construction so it can be overridden
CFLAGS currently takes care of two aspects of the build: optimisation
and debug symbols on one hand, the include path on the other. The
former should be overridable by users, the latter shouldn't.
This patch moves the include path flag to CPPFLAGS, which is
appropriate for pre-processor directives. This leaves CFLAGS with only
overridable flags.
Based on a patch by Roflcopter4:
https://github.com/joncampbell123/dosbox-x/pull/3850
Signed-off-by: Stephen Kitt <steve@sk2.org>
Stephen Kitt