fix python version check

The python code that is used to determine the version number
did not work with python3.
In python3 print is a real function and must be called as such.
Use positional accessors to be compatible with python < 2.6.
Also extend the error message for users that attempt the build
with python3.

Task-number: QTBUG-48507
Change-Id: I49e1fb77c2cc421ac1faed8d8143bf605fbde700
Reviewed-by: Florian Bruhin <[email protected]>
Reviewed-by: Michael Brüning <[email protected]>

Author: jobor

tools/qmake/mkspecs/features/functions.prf

@@ -22,11 +22,18 @@ defineTest(isPlatformSupported) {
 }
 
 defineTest(isPythonVersionSupported) {
-  python_major_version = $$system('python -c "import sys; print sys.version_info.major"')
-  python_minor_version = $$system('python -c "import sys; print sys.version_info.minor"')
-  lessThan(python_major_version, 3): greaterThan(python_major_version, 1): greaterThan(python_minor_version, 6): return(true)
-  skipBuild("Using Python version "$$python_major_version"."$$python_minor_version", but Python version 2 (2.7 or later) is required to build Qt WebEngine.")
-  return(false)
+    python_error_msg = "Python version 2 (2.7 or later) is required to build Qt WebEngine."
+    python_major_version = $$system('python -c "import sys; print(sys.version_info[0])"')
+    greaterThan(python_major_version, 2) {
+        skipBuild("Python version 3 is not supported by Chromium.")
+        skipBuild($$python_error_msg)
+        return(false)
+    }
+    python_minor_version = $$system('python -c "import sys; print(sys.version_info[1])"')
+    greaterThan(python_major_version, 1): greaterThan(python_minor_version, 6): return(true)
+    skipBuild("Using Python version "$$python_major_version"."$$python_minor_version".")
+    skipBuild($$python_error_msg)
+    return(false)
 }
 
 defineTest(isGCCVersionSupported) {