mesa/llvm: use llvm-config --cppflags

Use --cppflags instead of --cflags so that we get the -I and -D flags
we want, but not compiler options like -O3.

A similar change should probably be made for autoconf.

configs/linux-llvm

 OPT_FLAGS = -O3 -ansi -pedantic
 ARCH_FLAGS = -mmmx -msse -msse2 -mstackrealign
 
-DEFINES += -DNDEBUG -DGALLIUM_LLVMPIPE -DHAVE_UDIS86 \
-	-D__STDC_CONSTANT_MACROS -D__STDC_LIMIT_MACROS
+DEFINES += -DNDEBUG -DGALLIUM_LLVMPIPE -DHAVE_UDIS86
 
 # override -std=c99
 CFLAGS += -std=gnu99
 endif
 
 ifeq ($(MESA_LLVM),1)
-#  LLVM_CFLAGS=`llvm-config --cflags`
+  LLVM_CFLAGS=`llvm-config --cppflags`
   LLVM_CXXFLAGS=`llvm-config --cxxflags backend bitreader engine ipo interpreter instrumentation` -Wno-long-long
   LLVM_LDFLAGS = $(shell llvm-config --ldflags backend bitreader engine ipo interpreter instrumentation)
   LLVM_LIBS = $(shell llvm-config --libs backend bitwriter bitreader engine ipo interpreter instrumentation)