[flang] [llvm] [CMake] Fix using precompiled headers with ccache (PR #131397)

[Michael Kruse via llvm-commits]

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@@ -291,7 +291,7 @@ if(LLVM_CCACHE_BUILD)
       set_property(GLOBAL PROPERTY RULE_LAUNCH_COMPILE ${CCACHE_PROGRAM})
     else()
       if(LLVM_CCACHE_MAXSIZE OR LLVM_CCACHE_DIR OR
-         NOT LLVM_CCACHE_PARAMS MATCHES "CCACHE_CPP2=yes CCACHE_HASHDIR=yes")
+         NOT LLVM_CCACHE_PARAMS MATCHES "CCACHE_CPP2=yes CCACHE_HASHDIR=yes CCACHE_SLOPPINESS=pch_defines,time_macros")
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Meinersbur wrote:

If your Windows question was for this, I it will cause no cache hits because nothing sets `CCACHE_SLOPPINESS=pch_defines,time_macros`.

Workarounds could be 
1. `env` command from MSYS
2. `set` command from Windows itself (only a single variable per invocation and does not support specifying a command on the same line but can be  chained with `&&`): https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/set_1
3. emit a wrapper around `ccache` that sets those enviornment variables
4. test & abort if ccache does not use the required sloppiness option



https://github.com/llvm/llvm-project/pull/131397