qt5base-lts/mkspecs/features/toolchain.prf

defineReplace(qtMakeExpand) {
    out = "$$1"
    for(ever) {
        m = $$replace(out, ".*\\$\\(EXPORT_([^)]+)\\).*", \\1)
        equals(m, $$out): \
            return($$out)
        out = $$replace(out, "\\$\\(EXPORT_$$m\\)", $$eval($$m))
    }
}

isEmpty(QMAKE_DEFAULT_INCDIRS):!host_build {
    #
    # Get default include and library paths from compiler
    #
    gcc {
        !equals(QMAKE_HOST.os, Windows) {
            cmd_prefix = "LC_ALL=C"
            cmd_suffix = "</dev/null >/dev/null"
        } else {
            cmd_prefix = "set LC_ALL=C&"
            cmd_suffix = "<NUL >NUL"
        }
        output = $$system("$$cmd_prefix $$QMAKE_CXX $$qtMakeExpand($$QMAKE_CXXFLAGS) -xc++ -E -v - 2>&1 $$cmd_suffix", lines)
        add_includes = false
        for (line, output) {
            line ~= s/^ *//  # remove leading spaces
            contains(line, "LIBRARY_PATH=.*") {
                line ~= s/^LIBRARY_PATH=//  # remove leading LIBRARY_PATH=
                paths = $$split(line, $$QMAKE_DIRLIST_SEP)
                for (path, paths): \
                    QMAKE_DEFAULT_LIBDIRS += $$clean_path($$path)
            } else: contains(line, "$${LITERAL_HASH}include <.*") {  # #include <...> search starts here:
                add_includes = true
            } else: contains(line, "End of search.*") {
                add_includes = false
            } else: $$add_includes {
                !contains(line, ".* \\(framework directory\\)"): \
                    QMAKE_DEFAULT_INCDIRS += $$clean_path($$line)
            }
        }
        QMAKE_DEFAULT_LIBDIRS = $$unique(QMAKE_DEFAULT_LIBDIRS)
    } else: msvc {
        LIB = $$getenv("LIB")
        QMAKE_DEFAULT_LIBDIRS = $$split(LIB, $$QMAKE_DIRLIST_SEP)
        INCLUDE = $$getenv("INCLUDE")
        QMAKE_DEFAULT_INCDIRS = $$split(INCLUDE, $$QMAKE_DIRLIST_SEP)
    }

    unix {
        isEmpty(QMAKE_DEFAULT_INCDIRS): QMAKE_DEFAULT_INCDIRS = /usr/include /usr/local/include
        isEmpty(QMAKE_DEFAULT_LIBDIRS): QMAKE_DEFAULT_LIBDIRS = /lib /usr/lib
    }

    !isEmpty(QMAKE_DEFAULT_INCDIRS): cache(QMAKE_DEFAULT_INCDIRS, set stash)
    !isEmpty(QMAKE_DEFAULT_LIBDIRS): cache(QMAKE_DEFAULT_LIBDIRS, set stash)
}