all: switch to LLVM 9

azure-pipelines.yml

@@ -14,7 +14,7 @@ jobs:
     - task: CacheBeta@0
       displayName: Cache LLVM source
       inputs:
-        key: llvm-source-8-windows-v0
+        key: llvm-source-9-windows-v0
         path: llvm-project
     - task: Bash@3
       displayName: Download LLVM source
@@ -24,7 +24,7 @@ jobs:
     - task: CacheBeta@0
       displayName: Cache LLVM build
       inputs:
-        key: llvm-build-8-windows-v1
+        key: llvm-build-9-windows-v0
         path: llvm-build
     - task: Bash@3
       displayName: Build LLVM
@@ -34,6 +34,10 @@ jobs:
           if [ ! -f llvm-build/lib/liblldELF.a ]
           then
             choco install ninja
+            # LLVM 9 cannot be built with MinGW 8.
+            # For details: https://reviews.llvm.org/D70266
+            choco uninstall mingw
+            choco install mingw --version=7.3.0
             make llvm-build
           fi
     - task: Bash@3