mosh: fails with llvm

mosh fails to build with llvm-gcc. The original formula forced an
ENV.GCC_4_2, which broke under Xcode 4.2. Replace with fails_with_llvm.

It does build correctly with clang.

Closes Homebrew/homebrew#8336.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

Formula/mosh.rb

@@ -8,11 +8,9 @@ class Mosh < Formula
   depends_on 'gmp'
   depends_on 'oniguruma'
 
-  fails_with_llvm
+  fails_with_llvm "Inline asm errors"
 
   def install
-    ENV.gcc_4_2 # GCC > 4.0 required
-
     system "./configure", "--disable-debug", "--disable-dependency-tracking",
                           "--prefix=#{prefix}"
     system "make"