remove fails_with :gcc_4_2

Fixes #10

Author: tmcdonell

Formula/llvm-3.9.rb

@@ -91,7 +91,6 @@ class Llvm39 < Formula
   depends_on "cmake" => :build
 
   # requires gcc >= 4.7
-  fails_with :gcc_4_2
   ("4.3".."4.6").each do |n|
     fails_with :gcc => n
   end

Formula/llvm-4.0.rb

@@ -91,7 +91,6 @@ class Llvm40 < Formula
   depends_on "cmake" => :build
 
   # requires gcc >= 4.8
-  fails_with :gcc_4_2
   ("4.3".."4.7").each do |n|
     fails_with :gcc => n
   end

Formula/llvm-5.0.rb

@@ -93,7 +93,6 @@ class Llvm50 < Formula
   depends_on "cmake" => :build
 
   # requires gcc >= 4.8
-  fails_with :gcc_4_2
   ("4.3".."4.7").each do |n|
     fails_with :gcc => n
   end

Formula/llvm-6.0.rb

@@ -93,7 +93,6 @@ class Llvm60 < Formula
   depends_on "cmake" => :build
 
   # requires gcc >= 4.8
-  fails_with :gcc_4_2
   ("4.3".."4.7").each do |n|
     fails_with :gcc => n
   end

Formula/llvm-7.0.rb

@@ -93,7 +93,6 @@ class Llvm70 < Formula
   depends_on "cmake" => :build
 
   # requires gcc >= 4.8
-  fails_with :gcc_4_2
   ("4.3".."4.7").each do |n|
     fails_with :gcc => n
   end