Add ktx

ktx/external/astc-encoder/Source/cmake_compiler.cmake

@@ -0,0 +1,37 @@
+#  SPDX-License-Identifier: Apache-2.0
+#  ----------------------------------------------------------------------------
+#  Copyright 2020-2025 Arm Limited
+#
+#  Licensed under the Apache License, Version 2.0 (the "License"); you may not
+#  use this file except in compliance with the License. You may obtain a copy
+#  of the License at:
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#  License for the specific language governing permissions and limitations
+#  under the License.
+#  ----------------------------------------------------------------------------
+
+# On CMake 3.25 or older CXX_COMPILER_FRONTEND_VARIANT is not always set
+if(CMAKE_CXX_COMPILER_FRONTEND_VARIANT STREQUAL "")
+    set(CMAKE_CXX_COMPILER_FRONTEND_VARIANT "${CMAKE_CXX_COMPILER_ID}")
+endif()
+
+# Compiler accepts MSVC-style command line options
+set(is_msvc_fe "$<STREQUAL:${CMAKE_CXX_COMPILER_FRONTEND_VARIANT},MSVC>")
+# Compiler accepts GNU-style command line options
+set(is_gnu_fe1 "$<STREQUAL:${CMAKE_CXX_COMPILER_FRONTEND_VARIANT},GNU>")
+# Compiler accepts AppleClang-style command line options, which is also GNU-style
+set(is_gnu_fe2 "$<STREQUAL:${CMAKE_CXX_COMPILER_FRONTEND_VARIANT},AppleClang>")
+# Compiler accepts GNU-style command line options
+set(is_gnu_fe "$<OR:${is_gnu_fe1},${is_gnu_fe2}>")
+
+# Compiler is Visual Studio cl.exe
+set(is_msvccl "$<AND:${is_msvc_fe},$<CXX_COMPILER_ID:MSVC>>")
+# Compiler is Visual Studio clangcl.exe
+set(is_clangcl "$<AND:${is_msvc_fe},$<CXX_COMPILER_ID:Clang>>")
+# Compiler is upstream clang with the standard frontend
+set(is_clang "$<AND:${is_gnu_fe},$<CXX_COMPILER_ID:Clang,AppleClang>>")