Because the file is generated with -f using another Makefile, 2
different Makefiles are trying to handle the .meta file for the
target. The obvious .NOMETA_CMP or .NOMETA on the ${MAKE} targets
don't work as they are very limited in scope in bmake. Using
.PHONY fixes the problem and ensures that the ${MAKE} command
is always ran to check if it is outdated in the sub-make.
An example of the problem in gnu/lib/libgcc (with make -dM):
/usr/obj/root/git/freebsd/gnu/lib/libgcc/tm.h.meta: 2: a build command has changed
TARGET_CPU_DEFAULT="" HEADERS="options.h i386/biarch64.h i386/i386.h i386/unix.h i386/att.h dbxelf.h elfos-undef.h elfos.h freebsd-native.h freebsd-spec.h freebsd.h i386/x86-64.h i386/freebsd.h i386/freebsd64.h defaults.h" DEFINES="" /bin/sh /root/git/freebsd/gnu/lib/libgcc/../../../contrib/gcc/mkconfig.sh tm.h
vs
(cd /root/git/freebsd/gnu/lib/libgcc; make -f /root/git/freebsd/gnu/lib/libgcc/../../usr.bin/cc/cc_tools/Makefile MFILE=/root/git/freebsd/gnu/lib/libgcc/../../usr.bin/cc/cc_tools/Makefile GCCDIR=/root/git/freebsd/gnu/lib/libgcc/../../../contrib/gcc tm.h)
Skipping meta for tm.h: .NOMETA
(cd /root/git/freebsd/gnu/lib/libgcc; make -f /root/git/freebsd/gnu/lib/libgcc/../../usr.bin/cc/cc_tools/Makefile MFILE=/root/git/freebsd/gnu/lib/libgcc/../../usr.bin/cc/cc_tools/Makefile GCCDIR=/root/git/freebsd/gnu/lib/libgcc/../../../contrib/gcc tm.h)
`tm.h' is up to date.
Sponsored by: EMC / Isilon Storage Division
8a5f439677