BaseTools/footer.makefile: expand BUILD_CFLAGS last for C files too
BaseTools/footer.makefile: expand BUILD_CFLAGS last for C files too

BUILD_CPPFLAGS should be expanded before BUILD_CFLAGS. (The rule for C++
source files already does this, with BUILD_CPPFLAGS and BUILD_CXXFLAGS.)

This patch doesn't change behavior.

Cc: Liming Gao <6480311aeeb4b006862f6d13ebabddc03f51e507@intel.com>
Cc: Yonghong Zhu <78d981fe33a016071af5222c56d5cf77f30fb0b2@intel.com>
Ref: https://bugzilla.redhat.com/show_bug.cgi?id=1540244
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <7437296077edea1cb64451c122c4dac071f0cfbc@redhat.com>
Reviewed-by: Liming Gao <6480311aeeb4b006862f6d13ebabddc03f51e507@intel.com>

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