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>

--- gcc-4.0.0/libstdc++-v3/configure-old	2005-04-30 22:04:48.061603912 -0500

+++ gcc-4.0.0/libstdc++-v3/configure	2005-04-30 22:06:13.678588152 -0500

@@ -7194,6 +7194,9 @@

 cat >>conftest.$ac_ext <<_ACEOF

 /* end confdefs.h.  */

 #include <complex.h>

+#ifdef __UCLIBC__

+#error ugly hack to make sure configure test fails here for cross until uClibc supports the complex funcs

+#endif

 int

 main ()

 {