build: -D/-I arguments go into CPPFLAGS

build: -D/-I arguments go into CPPFLAGS

-D and -I are preprocessor directives, they are therefore to appear
in CPPFLAGS, not CFLAGS. (It is unfortunate that pkg-config does not
make the distinction / or it was misnamed, because only -D/-I make
sense to be emitted by pkg-config in the first place — anything else
(-f/-m) has the potential to mess up someone's compilation. So
pkg-config's Cflags is actually used to convery Cppflags.)

Change-Id: I7031834ae2d9446367ce02ca78be9842dece0683
Signed-off-by: himanshu <h.himanshu@samsung.com>