Fix AzAutoGen output to use a proper output using path.commonpath instead of path.commonprefix, which unlike commonprefix always return a valid path. For example, commonprefix [usr/hello.txt, usr/helium.cpp] would return usr/he

Signed-off-by: Gene Walters <genewalt@amazon.com>

cmake/AzAutoGen.py

@@ -71,10 +71,10 @@ def SearchPaths(filename, paths=[]):
     return None
 
 def ComputeOutputPath(inputFiles, projectDir, outputDir):
-    commonInputPath = os.path.commonprefix(inputFiles) # If we've globbed many source files, this finds the common prefix
+    commonInputPath = os.path.commonpath(inputFiles) # If we've globbed many source files, this finds the common path
     if os.path.isfile(commonInputPath): # If the commonInputPath resolves to an actual file, slice off the filename
         commonInputPath = os.path.dirname(commonInputPath)
-    commonPath = os.path.commonprefix([commonInputPath, projectDir]) # Finds the common path between the data source files and our project directory (//depot/dev/Code/Framework/AzCore/)
+    commonPath = os.path.commonpath([commonInputPath, projectDir]) # Finds the common path between the data source files and our project directory (//depot/dev/Code/Framework/AzCore/)
     inputRelativePath = os.path.relpath(commonInputPath, commonPath) # Computes the relative path for the project source directory (Code/Framework/AzCore/AutoGen/)
     return os.path.join(outputDir, inputRelativePath) # Returns a suitable output directory (//depot/dev/Generated/Code/Framework/AzCore/AutoGen/)