Disable Clang warning -Wexit-time-destructors.

This warns on `static const std::map<...>`.

re2c is single-threaded, so there's no risk of race conditions when one
thread is terminating and the other one tries to access the object.

cmake/Re2cCompilerFlags.cmake

@@ -53,6 +53,8 @@ if (NOT CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
         # re2c uses C++11, not C++98
         "-Wno-c++98-compat"
         "-Wno-c++98-compat-pedantic"
+        # re2c is single-threaded => no danger of race conditions
+        "-Wno-exit-time-destructors"
     )
     try_cxxflag("-fdiagnostics-color=always")
 

configure.ac

@@ -188,6 +188,7 @@ TRY_CXXFLAG([-Weverything], m4_join([ ],
     [-Wno-c++98-compat-pedantic],
     [-Wno-unsafe-pointer-arithmetic],
     [-Wno-unsafe-buffer-usage],
+    [-Wno-exit-time-destructors], dnl re2c is single-threaded => no danger of race conditions
     [-Wno-switch-enum]))