Fixes Visual Studio 2015 parallel builds (-j switch)

Reference: http://stackoverflow.com/questions/284778/what-are-the-implications-of-using-zi-vs-z7-for-visual-studio-c-projects

fatal error C1041: cannot open program database 'C:\godot\vc140.pdb'; if multiple CL.EXE write to the same .PDB file, please use /FS

platform/windows/detect.py

@@ -203,14 +203,14 @@ def configure(env):
 			env.Append(LINKFLAGS=['/SUBSYSTEM:CONSOLE'])
 		elif (env["target"]=="debug_release"):
 
-			env.Append(CCFLAGS=['/Zi','/Od'])
+			env.Append(CCFLAGS=['/Z7','/Od'])
 			env.Append(LINKFLAGS=['/DEBUG'])
 			env.Append(LINKFLAGS=['/SUBSYSTEM:WINDOWS'])
 			env.Append(LINKFLAGS=['/ENTRY:mainCRTStartup'])
 
 		elif (env["target"]=="debug"):
 
-			env.Append(CCFLAGS=['/Zi','/DDEBUG_ENABLED','/DDEBUG_MEMORY_ENABLED','/DD3D_DEBUG_INFO','/Od'])
+			env.Append(CCFLAGS=['/Z7','/DDEBUG_ENABLED','/DDEBUG_MEMORY_ENABLED','/DD3D_DEBUG_INFO','/Od'])
 			env.Append(LINKFLAGS=['/SUBSYSTEM:CONSOLE'])
 			env.Append(LINKFLAGS=['/DEBUG'])