Use gcc trunk for clang-tidy (#4262)

This seems like the better of the alternatives,
but happy to change if anyone thinks otherwise

Closes #4092

etc/config/c++.amazon.properties

@@ -3109,7 +3109,7 @@ tools.clangtidytrunk.name=clang-tidy (trunk)
 tools.clangtidytrunk.type=independent
 tools.clangtidytrunk.class=clang-tidy-tool
 tools.clangtidytrunk.exclude=cl19:cl_new
-tools.clangtidytrunk.options=--gcc-toolchain=/opt/compiler-explorer/gcc-9.2.0
+tools.clangtidytrunk.options=--gcc-toolchain=/opt/compiler-explorer/gcc-snapshot
 tools.clangtidytrunk.stdinHint=disabled
 
 tools.iwyu.exe=/opt/compiler-explorer/iwyu/0.12/bin/include-what-you-use