The LLVM backend now only works with 2.9+, don't try it if we have 2.7

This fix is very wrong, but I'm drowning in optllvm failures and need
to fix this ASAP (it's somewhat suboptimal that I won't be able to run
the LLVM tests here until I upgrade the OS or install a later LLVM
manually).

testsuite/mk/test.mk

@@ -86,11 +86,17 @@ else
 RUNTEST_OPTS += -e ghc_with_smp=0
 endif
 
-ifneq "$(shell $(SHELL) -c 'llvmc --version | grep version' 2> /dev/null)" ""
+LLVM_VERSION = $(shell $(SHELL) -c "llvmc --version | grep version | sed 's/^.*version \([0-9]*\)\.\([0-9]*\).*$$/\1\.\2/'" 2> /dev/null)
+
+ifneq "$(LLVM_VERSION)" ""
+ifneq "$(LLVM_VERSION)" "2.7"
 RUNTEST_OPTS += -e ghc_with_llvm=1
 else
 RUNTEST_OPTS += -e ghc_with_llvm=0
 endif
+else
+RUNTEST_OPTS += -e ghc_with_llvm=0
+endif
 
 ifeq "$(WINDOWS)" "YES"
 RUNTEST_OPTS += -e windows=True