make the name of the library directory a config option

Introduce new makefile variable lib to hold the name of the lib
directory ("lib" by default).  Also introduce a switch for configure
to specify this name with --with-lib=ARG.  This is useful for systems
that use a different name than "lib" (like "lib64" on some 64 bit
Linux architectures).

Signed-off-by: Robert Schiele <rschiele@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/configure.ac b/configure.ac
index b2f1965..84fd7f1 100644
--- a/configure.ac
+++ b/configure.ac
@@ -69,6 +69,17 @@
 ## Site configuration related to programs (before tests)
 ## --with-PACKAGE[=ARG] and --without-PACKAGE
 #
+# Set lib to alternative name of lib directory (e.g. lib64)
+AC_ARG_WITH([lib],
+ [AS_HELP_STRING([--with-lib=ARG],
+                 [ARG specifies alternative name for lib directory])],
+ [if test "$withval" = "no" -o "$withval" = "yes"; then \
+	AC_MSG_WARN([You should provide name for --with-lib=ARG]); \
+else \
+	GIT_CONF_APPEND_LINE(lib=$withval); \
+fi; \
+],[])
+#
 # Define SHELL_PATH to provide path to shell.
 GIT_ARG_SET_PATH(shell)
 #