Add new macro IN_MODULE to identify module in which source is built

The current scheme to identify which module a translation unit is
built in depends on defining multiple macros IS_IN_* and also defining
NOT_IN_libc if we're building a non-libc module.  In addition, there
is an IN_LIB macro that does effectively the same thing, but for
different modules (notably the systemtap probes).  This macro scheme
unifies both ideas to use just one macro IN_MODULE and assign it a
value depending on the module it is being built into.  If the module
is not defined, it defaults to MODULE_libc.

Patches that follow will replace uses of IS_IN_* variables with the
IS_IN() macro.  libc-symbols.h has been converted already to give an
example of how such a transition will look.

Verified that there are no relevant binary changes.  One source change
that will crop up repeatedly is that of nscd_stat, since it uses the
build timestamp as a constant in its logic.

	* Makeconfig (in-module): Get value of libof set for the
	translation unit.
	(CPPFLAGS): Use $(in-module).
	* Makerules: Don't suffix routine names for nonlib.
	* include/libc-modules.h: New file.
	* include/libc-symbols.h: Include libc-modules.h
	(IS_IN): New macro to replace IS_IN_* macros.
	* elf/Makefile: Set libof-* for each routine.
	* elf/rtld-Rules: Likewise.
	* extra-modules.mk: Likewise.
	* iconv/Makefile: Likewise.
	* iconvdata/Makefile: Likewise.
	* locale/Makefile: Likewise.
	* malloc/Makefile: Likewise.
	* nss/Makefile: Likewise.
	* sysdeps/gnu/Makefile: Likewise.
	* sysdeps/ieee754/ldbl-opt/Makefile: Likewise.
	* sysdeps/unix/sysv/linux/Makefile: Likewise.
	* sysdeps/s390/s390-64/Makefile: Likewise.
	* nscd/Makefile: Set libof-* for each routine.  Set CFLAGS and
	CPPFLAGS for nscd instead of nonlib.

malloc/Makefile

@@ -89,6 +89,11 @@ endif
 do-memusagestat: $(objpfx)memusagestat
 
 memusagestat-modules = memusagestat
+
+cpp-srcs-left := $(memusagestat-modules)
+lib := memusagestat
+include $(patsubst %,$(..)cppflags-iterator.mk,$(cpp-srcs-left))
+
 $(objpfx)memusagestat: $(memusagestat-modules:%=$(objpfx)%.o)
 	$(LINK.o) -o $@ $^ $(libgd-LDFLAGS) -lgd -lpng -lz -lm