Compiler version string.
Compiler version in major[.minor[.patch[.tweak]]] format. This variable is not guaranteed to be defined for all compilers or languages.
For example CMAKE_C_COMPILER_VERSION and CMAKE_CXX_COMPILER_VERSION might indicate the respective C and C++ compiler version.
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https://cmake.org/cmake/help/v3.19/variable/CMAKE_LANG_COMPILER_VERSION.html