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 -durN gcc-4.4.5.orig/libiberty/Makefile.in gcc-4.4.5/libiberty/Makefile.in

--- gcc-4.4.5.orig/libiberty/Makefile.in	2008-10-22 15:30:19.000000000 +0200

+++ gcc-4.4.5/libiberty/Makefile.in	2010-10-09 23:02:28.000000000 +0200

@@ -227,6 +227,7 @@

 	  $(AR) $(AR_FLAGS) $(TARGETLIB) \

 	    $(REQUIRED_OFILES) $(EXTRA_OFILES) $(LIBOBJS); \

 	  $(RANLIB) $(TARGETLIB); \

+	  cp $(TARGETLIB) ../ ; \

 	  cd ..; \

 	else true; fi