cmake/make: use -isystem for system libc headers

using -isystem for the libc standard include directory is the only way
to make it the first candidate for #include <foo> path search, and to
suppress warnings when building 3rd party code including them.

src/base/build.mak

@@ -27,10 +27,10 @@ FIXUP    = psp-fixup-imports
 ENC		 = PrxEncrypter
 
 # Add PSPSDK includes and libraries.
-INCDIR   := $(INCDIR) . $(PSPDEV)/psp/include $(PSPSDK)/include
+INCDIR   := $(INCDIR) . $(PSPSDK)/include
 LIBDIR   := $(LIBDIR) . $(PSPDEV)/psp/lib $(PSPSDK)/lib
 
-CFLAGS   := $(addprefix -I,$(INCDIR)) $(CFLAGS)
+CFLAGS   := -isystem $(PSPDEV)/psp/include $(addprefix -I,$(INCDIR)) $(CFLAGS)
 CXXFLAGS := $(CFLAGS) $(CXXFLAGS)
 ASFLAGS  := $(CFLAGS) $(ASFLAGS)
 

src/base/pspdev.cmake

@@ -9,8 +9,8 @@ SET(CMAKE_SYSTEM_VERSION 1)
 SET(CMAKE_SYSTEM_PROCESSOR mips)
 SET(CMAKE_C_COMPILER psp-gcc)
 SET(CMAKE_CXX_COMPILER psp-g++)
-SET(CMAKE_C_FLAGS_INIT "-I${PSPDEV}/psp/include -I${PSPDEV}/psp/sdk/include -DPSP")
-SET(CMAKE_CXX_FLAGS_INIT "-I${PSPDEV}/psp/include -I${PSPDEV}/psp/sdk/include -DPSP")
+SET(CMAKE_C_FLAGS_INIT "-isystem ${PSPDEV}/psp/include -I${PSPDEV}/psp/sdk/include -DPSP")
+SET(CMAKE_CXX_FLAGS_INIT "-isystem ${PSPDEV}/psp/include -I${PSPDEV}/psp/sdk/include -DPSP")
 SET(CMAKE_EXE_LINKER_FLAGS_INIT "-L${PSPDEV}/lib -L${PSPDEV}/psp/lib -L${PSPDEV}/psp/sdk/lib -Wl,-zmax-page-size=128")
 #SET(CMAKE_SHARED_LINKER_FLAGS_INIT "...")
 #SET(CMAKE_STATIC_LINKER_FLAGS_CONFIG_INIT "...")