Fix --enable-profiling bug introduced by 2013-02-25 change.

Fix --enable-profiling bug introduced by 2013-02-25 change.

This bug was introduced by my 2013-02-25 change that simplified
data_start configuration.  Without this change, on GNU/Linux
an Emacs configured with --enable-profiling fails immediately
due to a profiler signal.
* configure.ac (LD_SWITCH_SYSTEM_TEMACS): Append -pg if profiling
and if not on GNU/Linux or FreeBSD.
* lib/Makefile.am (AM_CFLAGS): Add $(PROFILING_CFLAGS), so that
lib/*.o is profiled too.
* src/Makefile.in: Compile with $(PROFILING_CFLAGS), but do not link
with these flags.  On platforms where special flags are needed
when linking temacs, the flags are now in LD_SWITCH_SYSTEM_TEMACS.
(ALL_CFLAGS): Remove $(PROFILING_CFLAGS).
(.c.o, .m.o): Compile with $(PROFILING_CFLAGS).