Disable -Wuninitialized for gcc

If the compiler is gcc, disable variants of -Wuninitialized depending
on the gcc version.  This gets a lot of false positive warnings out of
the build.

Generate a new configure for the gcc -Wno-uninitialized fix.

Pick up -Wno-uninitialized from configure

Add the option -Wno[-maybe]-uninitialized as determined by configure.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@172006 91177308-0d34-0410-b5e6-96231b3b80d8