Add premake cmake generator.

`./build/CMakeLists.txt` is generated by `./xb.bat premake --devenv=cmake` and enables use of other IDEs like `CLion` for example.

.gitmodules

@@ -64,3 +64,6 @@
 [submodule "third_party/DirectXShaderCompiler"]
 	path = third_party/DirectXShaderCompiler
 	url = https://github.com/microsoft/DirectXShaderCompiler.git
+[submodule "third_party/premake-cmake"]
+	path = third_party/premake-cmake
+	url = https://github.com/Enhex/premake-cmake.git

premake5.lua

@@ -1,5 +1,6 @@
 include("tools/build")
 require("third_party/premake-export-compile-commands/export-compile-commands")
+require("third_party/premake-cmake/cmake")
 
 location(build_root)
 targetdir(build_bin)

xenia-build

@@ -372,9 +372,9 @@ def run_platform_premake(cc='clang', devenv=None):
         if 'VSVERSION' in os.environ:
             vs_version = os.environ['VSVERSION']
 
-        return run_premake('windows', 'vs' + vs_version)
+        return run_premake('windows', devenv or ('vs' + vs_version))
     else:
-        return run_premake('linux', devenv == 'codelite' and devenv or 'gmake2', cc)
+        return run_premake('linux', devenv or 'gmake2', cc)
 
 
 def run_premake_export_commands():