configure: Support the = prefix for -I and -L

For gcc's -I and -L arguments a = prefix is replaced by the sysroot.
Since we're resolving include paths and library paths, we have to
support this feature.

For example, the linux-rasp-pi3-g++ makes use of this and is broken
without this patch.

Change-Id: Ie39e63322bd35e2a93aa8e55d52260164b8c6a6b
Reviewed-by: Kai Koehne <kai.koehne@qt.io>

mkspecs/features/qt_configure.prf

@@ -515,6 +515,17 @@ defineTest(qtConfSetupLibraries) {
     }
 }
 
+defineReplace(qtGccSysrootifiedPath) {
+    return($$replace(1, ^=, $$[QT_SYSROOT]))
+}
+
+defineReplace(qtGccSysrootifiedPaths) {
+    sysrootified =
+    for (path, 1): \
+        sysrootified += $$qtGccSysrootifiedPath($$path)
+    return($$sysrootified)
+}
+
 # libs-var, libs, in-paths, out-paths-var
 defineTest(qtConfResolveLibs) {
     ret = true
@@ -531,6 +542,7 @@ defineTest(qtConfResolveLibs) {
             out += $$l
         } else: contains(l, "^-L.*") {
             lp = $$replace(l, "^-L", )
+            gcc: lp = $$qtGccSysrootifiedPath($$lp)
             !exists($$lp/.) {
                 qtLog("Library path $$val_escape(lp) is invalid.")
                 ret = false
@@ -604,6 +616,7 @@ defineTest(qtConfResolveAllLibs) {
 # libs-var, in-paths, libs
 defineTest(qtConfResolvePathLibs) {
     ret = true
+    gcc: 2 = $$qtGccSysrootifiedPaths($$2)
     for (libdir, 2) {
         !exists($$libdir/.) {
             qtLog("Library path $$val_escape(libdir) is invalid.")
@@ -654,6 +667,7 @@ defineReplace(qtConfGetTestIncludes) {
 # includes-var, in-paths, test-object-var
 defineTest(qtConfResolvePathIncs) {
     ret = true
+    gcc: 2 = $$qtGccSysrootifiedPaths($$2)
     for (incdir, 2) {
         !exists($$incdir/.) {
             qtLog("Include path $$val_escape(incdir) is invalid.")