libclc: Use echo rather than true for try_compile

[daniels]

Summary

When providing a fake compiler, libclc currently uses 'true' which does
not exist on Windows. Use echo instead as the no-op.

Depends on: D77162

[jvesely]

This will add noise to CMakeOutput.log and CMakeError.log, but I guess it's just one line.

[daniels]

rebase

libclc/cmake/CMakeTestCLCCompiler.cmake

 if(NOT CMAKE_CLC_COMPILER_WORKS)
   PrintTestCompilerStatus("CLC" "")
   file(WRITE ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/testCLCCompiler.cl
     "__kernel void test_k(global int * a)\n"
     "{ *a = 1; }\n")
   try_compile(CMAKE_CLC_COMPILER_WORKS ${CMAKE_BINARY_DIR}
     ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/testCLCCompiler.cl
     # We never generate executable so bypass the link step
-    CMAKE_FLAGS -DCMAKE_CLC_LINK_EXECUTABLE='true'
+    CMAKE_FLAGS -DCMAKE_CLC_LINK_EXECUTABLE='echo'
     OUTPUT_VARIABLE __CMAKE_CLC_COMPILER_OUTPUT)
   # Move result from cache to normal variable.
   set(CMAKE_CLC_COMPILER_WORKS ${CMAKE_CLC_COMPILER_WORKS})
   unset(CMAKE_CLC_COMPILER_WORKS CACHE)
   set(CLC_TEST_WAS_RUN 1)
 endif()
 
 if(NOT CMAKE_CLC_COMPILER_WORKS)

libclc/cmake/CMakeTestLLAsmCompiler.cmake

 if(NOT CMAKE_LLAsm_COMPILER_WORKS)
   PrintTestCompilerStatus("LLAsm" "")
   file(WRITE ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/testLLAsmCompiler.ll
     "define i32 @test() {\n"
     "ret i32 0 }\n" )
   try_compile(CMAKE_LLAsm_COMPILER_WORKS ${CMAKE_BINARY_DIR}
     ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/testLLAsmCompiler.ll
     # We never generate executable so bypass the link step
-    CMAKE_FLAGS -DCMAKE_LLAsm_LINK_EXECUTABLE='true'
+    CMAKE_FLAGS -DCMAKE_LLAsm_LINK_EXECUTABLE='echo'
     OUTPUT_VARIABLE __CMAKE_LLAsm_COMPILER_OUTPUT)
   # Move result from cache to normal variable.
   set(CMAKE_LLAsm_COMPILER_WORKS ${CMAKE_LLAsm_COMPILER_WORKS})
   unset(CMAKE_LLAsm_COMPILER_WORKS CACHE)
   set(LLAsm_TEST_WAS_RUN 1)
 endif()
 
 if(NOT CMAKE_LLAsm_COMPILER_WORKS)