Add -MP with -MMD

This creates a .PHONY target for each file so that if a header is
renamed, the impact will be the files that include it being rebuilt
instead of the previous behaviour where the build would simply fail
and complain that the file doesn't exist.

src/build/Common.gmake

@@ -173,7 +173,7 @@ ifdef WALL
 endif
 
 # Compiler-specific options
-CFLAGS	+=	-MMD
+CFLAGS	+=	-MMD -MP
 CC		?=	gcc
 CCPRE	?= ${shell if [ `echo __clang__ | $(CC) -E - | grep -v '^\#'` != __clang__ ] ; then echo clang ; elif [ `echo __INTEL_COMPILER | $(CC) -E - | grep -v '^\#'` != __INTEL_COMPILER ] ; then echo icc ; else echo gcc ; fi}
 ifeq ($(CCPRE),clang)