gallium: Fix build when exiting CFLAGS contains a path with different gl.h

If a path is in CFLAGS when building and that path contains gl.h
then the wrong gl.h is used when building. This can lead to very
confusing errors. The solution is rather than postpend the CFLAGS
we prepend the paths as expected allowing compilation to occur
as intended

Signed-off-by: Benjamin Close <Benjamin.Close@clearchain.com>

src/gallium/state_trackers/egl/Makefile

@@ -6,14 +6,15 @@ TOP        = ../../../..
 
 include ${TOP}/configs/current
 
-CFLAGS += -g -Wall -Werror-implicit-function-declaration -fPIC \
+CFLAGS:= -g -Wall -Werror-implicit-function-declaration -fPIC \
           -I${GALLIUMDIR}/include \
           -I${GALLIUMDIR}/auxiliary \
           -I${TOP}/src/mesa/drivers/dri/common \
           -I${TOP}/src/mesa \
           -I$(TOP)/include \
           -I$(TOP)/src/egl/main \
-          ${LIBDRM_CFLAGS}
+          ${LIBDRM_CFLAGS} \
+          ${CFLAGS}
 
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