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Upgraded from 3.14 to 3.18 (and 3.19) via scoop recently and broke my privately maintained version of the pthreads4w library. This library uses a single source file, pthread.c, with different compile-time constants to produce different versions of the library, depending on how thread cleanup is done. One of the versions should compile pthread.c as C++ source, which used to be possible in the MSVC path by adding /TP via target_compile_options. However, it's now the case that /TC is hardwired into the CMake source and /TP seems to be silently stripped (or ignored).

I've tried setting the target's linker language, as this seems to be a default suggested by the source. (The symlink suggestion posed on Stackoverflow is unreliable on Windows.)

What's the preferred way to compile C and C++ source with 3.18/19? Is this a feature or bug?

Code snippet from the CMakeLists.txt

cmake_minimum_required(VERSION 3.14)
project(pthreads4w VERSION ${PTHREADS4W_VERSION} LANGUAGES C CXX)

## ...

set(VCEFLAGS)
if(MSVC)
    if(MSVC_VERSION EQUAL 1200)
        set(VCEFLAGS  "/EHa" "/TP")
    else()
        set(VCEFLAGS  "/EHs" "/TP")
    endif()

    set(build_defines ${build_defines} HAVE_CONFIG_H __PTW32_RC_MSC)
elseif (${CMAKE_C_COMPILER_ID} STREQUAL "GNU")
    set(build_defines ${build_defines} HAVE_CONFIG_H)
endif()

## ...

function(shared_lib type def)
    set(targ pthread${type}${PTW32_VER})
    add_library(${targ} SHARED pthread.c ${CMAKE_BINARY_DIR}/version.rc)
    message(STATUS ${targ})
    target_compile_definitions(${targ} PRIVATE ${def} ${build_defines} __PTW32_BUILD_INLINED)
    set_target_properties(${targ} PROPERTIES DEBUG_POSTFIX "d")

    if (MSVC)
      # Set resource compiler definition...
      target_compile_definitions(${targ} PRIVATE __PTW32_RC_MSC)
    endif ()
    if (${type} STREQUAL "VCE")
        ## Should set "/TP" here, but it's either silently stripped or ignored
        set_target_properties(${targ} PROPERTIES LINKER_LANGUAGE CXX)
        target_compile_options(${targ} PUBLIC "${VCEFLAGS}")
    elseif (${CMAKE_C_COMPILER_ID} STREQUAL "GNU")
	target_compile_options(${targ} PRIVATE "-mthreads")
	if (${type} STREQUAL "GCE")
            set_target_properties(${targ} PROPERTIES LINKER_LANGUAGE CXX)
	    target_compile_options(${targ} PRIVATE "-xc++")
	    target_link_libraries(${targ} stdc++)
	    target_link_options(${targ} PRIVATE "-shared-libgcc")
	endif (${type} STREQUAL "GCE")
    endif (${type} STREQUAL "VCE")

    install(
      TARGETS ${targ}
      ARCHIVE # DESTINATION ${TARGET_ARCH}/${CONFIG}/lib
      LIBRARY # DESTINATION ${TARGET_ARCH}/${CONFIG}/lib
      RUNTIME # DESTINATION ${TARGET_ARCH}/${CONFIG}/bin
    )

    install(
        FILES $<TARGET_PDB_FILE:${targ}>
        CONFIGURATION Debug
        DESTINATION lib
        OPTIONAL
    )
endfunction()

if (MSVC)
  shared_lib ( VCE __PTW32_CLEANUP_CXX )
  shared_lib ( VSE __PTW32_CLEANUP_SEH )
  shared_lib ( VC  __PTW32_CLEANUP_C )
elseif (${CMAKE_C_COMPILER_ID} STREQUAL "GNU" OR ${CMAKE_C_COMPILER_ID} STREQUAL "Clang")
  ## NOTE: MinGW64 does support SEH exception handling, BUT it does not yet
  ## have the MSVC keywords "__try", "__except" and "__finally".
  shared_lib ( GCE __PTW32_CLEANUP_CXX )
  shared_lib ( GC  __PTW32_CLEANUP_C )
endif (MSVC)