Was using CPPFLAGS, but should use the explicit scons CCFLAGS which
makes it clear they are applied to both the C and C++ compiler.
CPPFLAGS was also fine (they are preprocessor flags, also applied to
both C and C++), but we should try to stay consistent with what we do
in Godot.
(cherry picked from commit f36acd8e31)
Split `targets` tool logic, moving all the compiler-specific flags to a
new `common_compiler_flags.py` file, and everything else (CPPDEFINES,
optimize option logic, dev build logic, etc) to the `godotcpp` tool.
The default tools now apply the common compiler flags by importing the
file and explicitly calling `configure`.
(cherry picked from commit 16df4bff30)
Fabio Alessandrelli
Thaddeus Crews