Makefile: use phony targets

Add 'build', 'build-*', and 'install' as phony targets to the top level
Makefile.

I tend to do everything in tree with the build in a directory called
'build'. This interfered with the target 'build', making it think the
target was up to date, and stopping scripts/crosstool-NG.sh from being
regenerated.

Added 'install' as I often set the prefix to $PWD/install.

Signed-off-by: Michael Hope <michael.hope@linaro.org>

diff -ru ltrace-0.5.3.org/Makefile.in ltrace-0.5.3/Makefile.in

--- ltrace-0.5.3.org/Makefile.in	2011-08-21 18:55:15.000000000 +0200

+++ ltrace-0.5.3/Makefile.in	2011-08-21 18:40:53.000000000 +0200

@@ -39,7 +40,7 @@

 		$(CC) $(LDFLAGS) $^ $(LIBS) -o $@

 libltrace.a: 	sysdeps/sysdep.o $(OBJ)

-		$(AR) rcv $@ $^

+		$(AR) rscv $@ $^

 $(OBJ):		sysdeps/sysdep.o