Added gitignore

.gitignore

+Release+Asserts
+*.inc
+Output
+*.o
+*.so
+.dir
+*.tmp
+*.cmi
+*.cmx
+llvm-install
+Makefile.config
+Makefile.llvmbuild
+META.llvm
+config.log
+config.status
+doxygen.cfg
+*.tar.gz
+*.def
+*.gen
+llvm.spec
+Makefile.common
+Makefile.llvm.config
+config.log
+config.status
+*.a
+cfg.foo.dot
+lit.site.cfg
+*.dot
+JITTests.exports
+llvm/include/llvm/Config/config.h
+llvm/include/llvm/Config/llvm-config.h
+llvm/include/llvm/Support/DataTypes.h