qt5base-lts/mkspecs/features/spec_post.prf

isEmpty(MAKEFILE_GENERATOR):error("Qmake spec does not set MAKEFILE_GENERATOR.")
isEmpty(QMAKE_PLATFORM) {
    isEmpty(TARGET_PLATFORM) {
        equals(MAKEFILE_GENERATOR, UNIX) {
            equals(QMAKE_HOST.os, Darwin): \
                TARGET_PLATFORM = macx
            else: \
                TARGET_PLATFORM = unix
        } else:if(equals(MAKEFILE_GENERATOR, MSVC.NET) \
                 |equals(MAKEFILE_GENERATOR, BMAKE) \
                 |equals(MAKEFILE_GENERATOR, MSBUILD) \
                 |equals(MAKEFILE_GENERATOR, MINGW)) {
            TARGET_PLATFORM = win32
        } else:if(equals(MAKEFILE_GENERATOR, PROJECTBUILDER) \
                 |equals(MAKEFILE_GENERATOR, XCODE)) {
        } else:equals(MAKEFILE_GENERATOR, GBUILD) {
            TARGET_PLATFORM = unix
        } else {
            error("Qmake spec sets an invalid MAKEFILE_GENERATOR.")
        }
    }
    equals(TARGET_PLATFORM, unix): \
        QMAKE_PLATFORM = unix
    else:equals(TARGET_PLATFORM, macx): \
        QMAKE_PLATFORM = mac macx unix
    else:equals(TARGET_PLATFORM, win32): \
        QMAKE_PLATFORM = win32
    else: \
        error("Qmake spec sets an invalid TARGET_PLATFORM.")
}
CONFIG += $$QMAKE_PLATFORM

isEmpty(QMAKE_COMPILER) {
    *-g++*: \
        QMAKE_COMPILER = gcc
    else:*-llvm*: \
        QMAKE_COMPILER = gcc llvm
    else:*-clang*: \
        QMAKE_COMPILER = clang llvm
    else:*-msvc*: \
        QMAKE_COMPILER = msvc
    else: \
        error("qmake spec does not announce the compiler family, and it cannot be guessed.")
    warning("qmake spec does not announce the compiler family. Guessed $${QMAKE_COMPILER}.")
}
CONFIG += $$QMAKE_COMPILER