[M4] Add missing compiler flag on Cray Compiler (#17604)

* [M4] Add missing compiler flag on Cray Compiler

The new version of the Cray Compiler are based on Clang, which means we
need to add the same LDFLAG as other clang environments.

var/spack/repos/builtin/packages/m4/package.py

@@ -36,6 +36,9 @@ def configure_args(self):
         spec = self.spec
         args = ['--enable-c++']
 
+        if spec.satisfies('%cce@9:'):
+            args.append('LDFLAGS=-rtlib=compiler-rt')
+
         if spec.satisfies('%clang') and not spec.satisfies('platform=darwin'):
             args.append('LDFLAGS=-rtlib=compiler-rt')