[PATCH] utils/unittest: Consistency of gtest and gtest_main libs.

$(llvm-config --libs | tr " " "\n" | grep gtest) returns:
-lgtest_main
-lgtest

instead of non-valid:
-lLLVMgtest_main
-lLLVMgtest

It also fixes:
$(ld): cannot find -lLLVMgtest
$(ld): cannot find -lLLVMgtest_main

Hi Johannes,

Applied a variation of this here:
  http://llvm.org/viewvc/llvm-project?view=rev&revision=146706

Thanks!
- Daniel