Do not validate file existence if path contains variables

We do not need to validate everything, while converting project
files. Some checks can be left to building step.

It fixes some false positive NOTFOUND errors.

Change-Id: I81ff2421fdea13add0bfc03086152a47bce39908
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

util/cmake/pro2cmake.py

@@ -166,6 +166,13 @@ def map_source_to_cmake(source: str, base_dir: str,
     if os.path.exists(os.path.join(base_dir, source)):
         return source
 
+    variable_pattern = re.compile(r'\$\{[A-Za-z0-9_]+\}')
+    match = re.match(variable_pattern, source)
+    if match:
+        # a complex, variable based path, skipping validation
+        # or resolving
+        return source
+
     for v in vpath:
         fullpath = os.path.join(v, source)
         if os.path.exists(fullpath):