Recognize Clang ASM support (#13473)

Since commit 571dc748 (Recognize Clang C and C++ compilers, 2010-05-17)
we recognize Clang C and C++ support.  Add Compiler/Clang-ASM.cmake to
enable use of Clang for ASM too.  Also teach Assembler test to try Clang
as an assembler.

Suggested-by: Tobias Pape <[email protected]>

Modules/Compiler/Clang-ASM.cmake

@@ -0,0 +1 @@
+include(Compiler/GNU-ASM)

Tests/Assembler/CMakeLists.txt

@@ -8,7 +8,7 @@ set(SRCS)
 # (at least) the following toolchains can process assembler files directly
 # and also generate assembler files from C:
 if("${CMAKE_GENERATOR}" MATCHES "Makefile")
-  if(("${CMAKE_C_COMPILER_ID}" MATCHES "^(GNU|HP|SunPro|XL)$") OR ("${CMAKE_C_COMPILER_ID}" STREQUAL "Intel"  AND  UNIX))
+  if(("${CMAKE_C_COMPILER_ID}" MATCHES "^(GNU|Clang|HP|SunPro|XL)$") OR ("${CMAKE_C_COMPILER_ID}" STREQUAL "Intel"  AND  UNIX))
     set(C_FLAGS "${CMAKE_C_FLAGS}")
     separate_arguments(C_FLAGS)
     set(SRCS main.s)