configure: pull ahead gcc-sysroot processing

the sysroot flags need to be established even before setting up the
spec, because as soon as that happens, toolchain.prf will try to
determine the default paths and cache them.

this also fixes sysroot use in toolchain flag support tests, which run
(somewhat) independently from the toolchain setup.

Task-number: QTBUG-63483
Change-Id: I7be1540e766dac58fb16f63176aa8d2879b51ae0
Reviewed-by: Joerg Bornemann <[email protected]>

configure.json

@@ -211,7 +211,7 @@
 
     "testTypeDependencies": {
         "linkerSupportsFlag": [ "use_gold_linker" ],
-        "verifySpec": [ "shared", "use_gold_linker", "compiler-flags", "gcc-sysroot", "qmakeargs", "commit" ],
+        "verifySpec": [ "shared", "use_gold_linker", "compiler-flags", "qmakeargs", "commit" ],
         "compile": [ "verifyspec" ],
         "detectPkgConfig": [ "cross_compile", "machineTuple" ],
         "library": [ "pkg-config" ],
@@ -518,6 +518,7 @@
 
     "features": {
         "prepare": {
+            "condition": "features.gcc-sysroot || true",
             "output": [ "prepareSpec", "prepareOptions", "preparePaths", "reloadSpec" ]
         },
         "machineTuple": {

configure.pri

@@ -1069,6 +1069,10 @@ defineTest(qtConfOutput_gccSysroot) {
         "\"QMAKE_LFLAGS += --sysroot=$$config.input.sysroot\""
     export(EXTRA_QMAKE_ARGS)
 
+    # This one is for qtConfToolchainSupportsFlag().
+    QMAKE_CXXFLAGS += --sysroot=$$config.input.sysroot
+    export(QMAKE_CXXFLAGS)
+
     output = \
         "!host_build {" \
         "    QMAKE_CFLAGS    += --sysroot=\$\$[QT_SYSROOT]" \

mkspecs/features/qt_configure.prf

@@ -344,7 +344,7 @@ defineReplace(qtConfToolchainSupportsFlag) {
     conftest = "int main() { return 0; }"
     write_file("$$test_out_dir/conftest.cpp", conftest)|error()
 
-    qtRunLoggedCommand("$$test_cmd_base $$QMAKE_CXX $${1} -o conftest-out conftest.cpp"): \
+    qtRunLoggedCommand("$$test_cmd_base $$QMAKE_CXX $$QMAKE_CXXFLAGS $${1} -o conftest-out conftest.cpp"): \
         return(true)
     return(false)
 }