Invert the tests on LLVMGCC_MAJVERS to check for value 4 instead of value

Invert the tests on LLVMGCC_MAJVERS to check for value 4 instead of value
3. This ensures that if llvm-gcc isn't available and consequently the value
of LLVMGCC_MAJVERS is blank, that the old (include runtime) behavior will
persist.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@27499 91177308-0d34-0410-b5e6-96231b3b80d8