Patch meson.build llvm config strategy (#20451)

This patch logic resovles a linking issue with ncurses in the mesa
package. This appears to be a recurring problem that was identified in
the mesa gitlab issues here:
https://gitlab.freedesktop.org/mesa/mesa/-/issues/2843

Using `_llvm_method = 'auto'` is broken. This patch replaces that with
`_llvm_method = 'config-tool'`, which is a hack, but makes it possible
to build.

I have commented on the closed issue (2843), referencing the original
author of the bug, and one of the mesa developers, so perhaps they will
fix the problem.

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

@@ -83,6 +83,12 @@ class Mesa(MesonPackage):
     # OpenGL ES requires OpenGL
     conflicts('~opengl +opengles')
 
+    def patch(self):
+        filter_file(
+            r"_llvm_method = 'auto'",
+            "_llvm_method = 'config-tool'",
+            "meson.build")
+
     def meson_args(self):
         spec = self.spec
         args = [