llvm: patch lldb for gcc-7 (#5239)

var/spack/repos/builtin/packages/llvm/llvm_gcc7.patch

@@ -0,0 +1,10 @@
+--- a/tools/lldb/include/lldb/Utility/TaskPool.h	2016-09-06 16:57:50.000000000 -0400
++++ b/tools/lldb/include/lldb/Utility/TaskPool.h	2017-08-29 16:29:41.448584015 -0400
+@@ -28,6 +28,7 @@
+ 
+ #include <cassert>
+ #include <cstdint>
++#include <functional>
+ #include <future>
+ #include <list>
+ #include <queue>

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

@@ -342,6 +342,9 @@ class Llvm(CMakePackage):
     conflicts('+clang_extra', when='~clang')
     conflicts('+lldb',        when='~clang')
 
+    # Github issue #4986
+    patch('llvm_gcc7.patch', when='@4.0.0:4.0.1+lldb %gcc@7.0:')
+
     def setup_environment(self, spack_env, run_env):
         spack_env.append_flags('CXXFLAGS', self.compiler.cxx11_flag)