Fixup some stray refs to gcc-8

azure-pipelines.yml

@@ -36,7 +36,7 @@ jobs:
     pool:
       vmImage: macOS-10.14
     steps:
-      - script: brew install gcc@9 ccache
+      - script: brew install gcc@8 gcc@9 ccache
         displayName: Prepare System
       - script: |
           set -eu

tests/deps/use-spdlog/gcc.tc.dds

@@ -1,4 +1,4 @@
 Compiler-ID: GNU
 C++-Version: C++17
-C++-Compiler: g++-8
+C++-Compiler: g++-9
 Flags: -D SPDLOG_COMPILED_LIB

tools/gcc-9.dds

@@ -3,5 +3,6 @@ C++-Version: C++17
 C-Compiler: gcc-9
 C++-Compiler: g++-9
 Flags: -D SPDLOG_COMPILED_LIB -fconcepts -Werror=return-type
+Link-Flags: -static-libgcc -static-libstdc++
 Debug:  True
 Compiler-Launcher: ccache