Bump LLVM version to 10.0

Fixes #18267.

.gitlab-ci.yml

@@ -838,6 +838,9 @@ validate-x86_64-linux-fedora27:
   stage: full-build
   image: "registry.gitlab.haskell.org/ghc/ci-images/x86_64-linux-fedora27:$DOCKER_REV"
   variables:
+    # LLVM 10 is not available for Fedora27
+    LLC: /bin/false
+    OPT: /bin/false
     TEST_ENV: "x86_64-linux-fedora27"
     BIN_DIST_PREP_TAR_COMP: "ghc-x86_64-fedora27-linux.tar.xz"
   cache:

configure.ac

@@ -715,7 +715,7 @@ AC_SUBST(InstallNameToolCmd)
 # tools we are looking for. In the past, GHC supported a number of
 # versions of LLVM simultaneously, but that stopped working around
 # 3.5/3.6 release of LLVM.
-LlvmVersion=9
+LlvmVersion=10
 AC_SUBST([LlvmVersion])
 sUPPORTED_LLVM_VERSION=$(echo \($LlvmVersion\) | sed 's/\./,/')
 AC_DEFINE_UNQUOTED([sUPPORTED_LLVM_VERSION], ${sUPPORTED_LLVM_VERSION}, [The supported LLVM version number])