Remove blacklists of old glib and gcc 4.8 debug builds

We never saw the same failure with gcc 4.8 debug builds with 55-based,
and the other failure suspected to related turned out not to be and
have been fixed.

So try to re-enable gcc 4.8 debug builds, and other old platforms but
explicitly disable gcc 4.9.1 which fails to compile Chromium.

Change-Id: Ib0a8ac33aafbd12d31e374dfd23f056b4ba1adf0
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

tools/qmake/mkspecs/features/configure.prf

@@ -57,7 +57,6 @@ defineTest(runConfigure) {
         }
         qtConfig(glib) {
              packagesExist("\'glib-2.0 >= 2.32.0\'"): WEBENGINE_CONFIG += use_glib
-             else: skipBuild("System glib is too old (min. version 2.32).$${EOL}")
         }
 
         for(package, $$list($$REQUIRED_PACKAGES)) {

tools/qmake/mkspecs/features/functions.prf

@@ -221,17 +221,15 @@ defineTest(isSanitizerLinuxClangVersionSupported) {
 }
 
 defineTest(isGCCVersionSupported) {
+  equals(QT_GCC_MAJOR_VERSION, 4):equals(QT_GCC_MINOR_VERSION, 9):lessThan(QT_GCC_PATCH_VERSION, 2) {
+    skipBuild("Gcc 4.9.1 fails to compile QtWebEngine, please use another gcc version.")
+    return(false)
+  }
   # The below will work for gcc 4.7 and up and also match gcc 5
-  CONFIG(release, debug|release): greaterThan(QT_GCC_MINOR_VERSION, 6):return(true)
+  greaterThan(QT_GCC_MINOR_VERSION, 6):return(true)
   greaterThan(QT_GCC_MAJOR_VERSION, 4):return(true)
 
-  # We need GCC 4.9 for debug builds because Skia handles SIMD inlines in headers poorly.
-  greaterThan(QT_GCC_MINOR_VERSION, 8):return(true)
-  CONFIG(debug, debug|release) {
-    skipBuild("Using gcc version "$$QT_GCC_MAJOR_VERSION"."$$QT_GCC_MINOR_VERSION", but at least gcc version 4.9 is required to build debug versions of Qt WebEngine.")
-  } else {
-    skipBuild("Using gcc version "$$QT_GCC_MAJOR_VERSION"."$$QT_GCC_MINOR_VERSION", but at least gcc version 4.7 is required to build Qt WebEngine.")
-  }
+  skipBuild("Using gcc version "$$QT_GCC_MAJOR_VERSION"."$$QT_GCC_MINOR_VERSION", but at least gcc version 4.7 is required to build Qt WebEngine.")
   return(false)
 }