[clang] [Clang][Driver] Warn on complex number range incompatibility with GCC (PR #144468)

[Shunsuke Watanabe via cfe-commits]

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@@ -520,6 +520,9 @@ def warn_drv_math_errno_enabled_after_veclib: Warning<
   "math errno enabled by '%0' after it was implicitly disabled by '%1',"
   " this may limit the utilization of the vector library">,
   InGroup<MathErrnoEnabledWithVecLib>;
+def warn_drv_gcc_incompatible_complex_range_override: Warning<
+  "combination of '%0' and '%1' results in complex number calculations incompatible with GCC">,
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s-watanabe314 wrote:

I understand that it's better to emit a single warning message. In that case, how about simply adding the "specify" part to the end of the original warning message? At least I think users would understand what to do.
`warning: combination of '-fcx-fortran-rules' and '-fcx-limited-range' results in complex number calculations incompatible with GCC. specify '-fcx-fortran-rules' after '-fcx-limited-range' for GCC compatibility [-Wgcc-compat] `

However, this warning message might be redundant because it's long and displays the same option twice. It might be better to use the following instead:
`warning: complex number calculation is incompatible with GCC. specify '-fcx-fortran-rules' after '-fcx-limited-range' for compatibility [-Wgcc-compat]`

https://github.com/llvm/llvm-project/pull/144468