llvm: fix build on 10.7 and 10.8

Closes #32495.

1 files changed, 7 insertions, 0 deletions

diff --git a/Library/Formula/llvm.rb b/Library/Formula/llvm.rb
index a66b30575..b8d8ac1d1 100644
--- a/Library/Formula/llvm.rb
+++ b/Library/Formula/llvm.rb
@@ -44,7 +44,14 @@ class Llvm < Formula
 
   keg_only :provided_by_osx
 
+  # Apple's libstdc++ is too old to build LLVM
+  fails_with :gcc
+  fails_with :llvm
+
   def install
+    # Apple's libstdc++ is too old to build LLVM
+    ENV.libcxx if ENV.compiler == :clang
+
     if build.with? "python" and build.include? 'disable-shared'
       raise 'The Python bindings need the shared library.'
     end