Merge pull request #13913 from carlocab/test-compiler

extend/ENV/std: ignore `fails_with` during `brew test`.

Library/Homebrew/extend/ENV/std.rb

@@ -57,7 +57,14 @@ module Stdenv
     # Os is the default Apple uses for all its stuff so let's trust them
     define_cflags "-Os #{SAFE_CFLAGS_FLAGS}"
 
-    send(compiler)
+    begin
+      send(compiler)
+    rescue CompilerSelectionError
+      # We don't care if our compiler fails to build the formula during `brew test`.
+      raise unless testing_formula
+
+      send(DevelopmentTools.default_compiler)
+    end
 
     return unless cc&.match?(GNU_GCC_REGEXP)