device: Introduce a qmake test function

A common issue for our users is that they do not provide the path
to their cross compiler or don't have it in their $PATH. Introduce
a qmake testFunction to sanity check the presence of the compiler.

Change-Id: I7d41db139d2a9c67334908b96e9f5e8f996426f6
Reviewed-by: Girish Ramakrishnan <girish.1.ramakrishnan@nokia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>

mkspecs/features/device_config.prf

@@ -25,3 +25,14 @@ exists($$DEVICE_PRI):include($$DEVICE_PRI)
 unset(DEVICE_PRI)
 unset(DIR)
 
+# Provide a function to be used by mkspecs
+defineTest(deviceSanityCheckCompiler) {
+    # Check if the binary exists, e.g. with an absolute path
+    exists($$QMAKE_CXX):return()
+
+    # Check if the compiler is in the path
+    system("which $$QMAKE_CXX > /dev/null"):return()
+
+    error("Compiler $$QMAKE_CXX not found")
+}
+