configure: auto detect dynamic library path switches

Most systems (e.g. Linux gcc) use "-Wl,-rpath," to pass to the linker the
runtime dynamic library paths. Some other systems (e.g. Sun, some BSD) use
"-R" etc. This patch adds tests in configure for the three most common
switches (to my best knowledge) which should cover all current platforms
where Git is used.

Signed-Off-By: Giovanni Funchal <gafunchal@gmail.com>

Signed-off-by: Junio C Hamano <gitster@pobox.com>

config.mak.in

@@ -3,6 +3,7 @@
 
 CC = @CC@
 CFLAGS = @CFLAGS@
+CC_LD_DYNPATH = @CC_LD_DYNPATH@
 AR = @AR@
 TAR = @TAR@
 #INSTALL = @INSTALL@		# needs install-sh or install.sh in sources

configure.ac

@@ -103,6 +103,38 @@ GIT_PARSE_WITH(tcltk))
 AC_MSG_NOTICE([CHECKS for programs])
 #
 AC_PROG_CC([cc gcc])
+# which switch to pass runtime path to dynamic libraries to the linker
+AC_CACHE_CHECK([if linker supports -R], ld_dashr, [
+   SAVE_LDFLAGS="${LDFLAGS}"
+   LDFLAGS="${SAVE_LDFLAGS} -R /"
+   AC_LINK_IFELSE(AC_LANG_PROGRAM([], []), [ld_dashr=yes], [ld_dashr=no])
+   LDFLAGS="${SAVE_LDFLAGS}"
+])
+if test "$ld_dashr" = "yes"; then
+   AC_SUBST(CC_LD_DYNPATH, [-R])
+else
+   AC_CACHE_CHECK([if linker supports -Wl,-rpath,], ld_wl_rpath, [
+      SAVE_LDFLAGS="${LDFLAGS}"
+      LDFLAGS="${SAVE_LDFLAGS} -Wl,-rpath,/"
+      AC_LINK_IFELSE(AC_LANG_PROGRAM([], []), [ld_wl_rpath=yes], [ld_wl_rpath=no])
+      LDFLAGS="${SAVE_LD_FLAGS}"
+   ])
+   if test "$ld_wl_rpath" = "yes"; then
+      AC_SUBST(CC_LD_DYNPATH, [-Wl,-rpath,])
+   else
+      AC_CACHE_CHECK([if linker supports -rpath], ld_rpath, [
+         SAVE_LDFLAGS="${LDFLAGS}"
+         LDFLAGS="${SAVE_LDFLAGS} -rpath /"
+         AC_LINK_IFELSE(AC_LANG_PROGRAM([], []), [ld_rpath=yes], [ld_rpath=no])
+         LDFLAGS="${SAVE_LD_FLAGS}"
+      ])
+      if test "$ld_rpath" = "yes"; then
+         AC_SUBST(CC_LD_DYNPATH, [-rpath])
+      else
+         AC_MSG_WARN([linker does not support runtime path to dynamic libraries])
+      fi
+   fi
+fi
 #AC_PROG_INSTALL		# needs install-sh or install.sh in sources
 AC_CHECK_TOOLS(AR, [gar ar], :)
 AC_CHECK_PROGS(TAR, [gtar tar])