[Bug modula2/107612] plugin/m2rte doesn't build on Mac OS X 10.7

["iains at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107612

--- Comment #10 from Iain Sandoe <iains at gcc dot gnu.org> ---
I fixed the plugin build to avoid linking libstdc++ (small additions to
Rainer's patch)

 *  linking libstdc++ causes the build to fail because the plugin cannot find
the libstdc++ because it is not yet installed.

 * it's not right to link it anyway - the plugin needs to resolve its symbols
from cc1gm2

Adding -nodefaultlibs fixes this + I adjusted the install name.
Actually, I do not think the rpaths are needed - because the plugin is
explicitly loaded - it does not need to find any dependent libs.

---- 

diff --git a/gcc/m2/Make-lang.in b/gcc/m2/Make-lang.in
index 0ea73e766d1..8d86c1371f3 100644
--- a/gcc/m2/Make-lang.in
+++ b/gcc/m2/Make-lang.in
@@ -36,7 +36,10 @@ ifeq (,$(findstring darwin,$(host)))
   soext=.so
 else
   soext=.dylib
-  PLUGINLDFLAGS=-Wl,-undefined,dynamic_lookup
+  PLUGINLDFLAGS = -Wl,-undefined,dynamic_lookup
+  PLUGINLDFLAGS += -Wl,-install_name,m2rte$(soext)
+  PLUGINLDFLAGS += -Wl,-rpath,@loader_path,-rpath,@loader_path/..
+  PLUGINLDFLAGS += -nodefaultlibs
 endif