[cmake] Use 'llvm-config --components' to determine components

[mgorny]

Summary

Use 'llvm-config --components' to determine available components rather
than relying on '--libs' to fail for non-available. This should fix
false positives when dylib is used.

Technically, it's a bug in llvm-config for '--libs' to return the dylib
for libraries that are not included in it. However, fixing this
triggers further bugs and it does not make much sense to put more effort
into this deprecated tool.

compiler-rt/cmake/Modules/CompilerRTUtils.cmake

if (LLVM_CONFIG_PATH)
     set(LLVM_BINARY_DIR ${BINARY_DIR} CACHE PATH "Path to LLVM build tree")
     set(LLVM_LIBRARY_DIR ${LIBRARY_DIR} CACHE PATH "Path to llvm/lib")
     set(LLVM_MAIN_SRC_DIR ${MAIN_SRC_DIR} CACHE PATH "Path to LLVM source tree")
     set(LLVM_TOOLS_BINARY_DIR ${TOOLS_BINARY_DIR} CACHE PATH "Path to llvm/bin")
     set(LLVM_INCLUDE_DIR ${INCLUDE_DIR} CACHE PATH "Paths to LLVM headers")
 
     # Detect if we have the LLVMXRay and TestingSupport library installed and
     # available from llvm-config.
+    set(COMPILER_RT_HAS_LLVMXRAY FALSE)
+    set(COMPILER_RT_HAS_LLVMTESTINGSUPPORT FALSE)
+
+    execute_process(
+      COMMAND ${LLVM_CONFIG_PATH} "--components"
+      RESULT_VARIABLE HAD_ERROR
+      OUTPUT_VARIABLE CONFIG_OUTPUT
+      ERROR_QUIET)
+    if (HAD_ERROR)
+      message(WARNING "llvm-config querying components failed with status ${HAD_ERROR}")
+    else()
+      string(REGEX REPLACE "[ \r\n\t]+" ";" CONFIG_OUTPUT ${CONFIG_OUTPUT})
+
+      list(FIND CONFIG_OUTPUT xray FOUND_XRAY)
+      if (NOT FOUND_XRAY EQUAL -1)
         execute_process(
           COMMAND ${LLVM_CONFIG_PATH} "--ldflags" "--libs" "xray"
           RESULT_VARIABLE HAD_ERROR
           OUTPUT_VARIABLE CONFIG_OUTPUT
           ERROR_QUIET)
         if (HAD_ERROR)
-      message(WARNING "llvm-config finding xray failed with status ${HAD_ERROR}")
-      set(COMPILER_RT_HAS_LLVMXRAY FALSE)
+          message(FATAL_ERROR "llvm-config finding xray failed with status ${HAD_ERROR}")
         else()
           string(REGEX REPLACE "[ \t]*[\r\n]+[ \t]*" ";" CONFIG_OUTPUT ${CONFIG_OUTPUT})
           list(GET CONFIG_OUTPUT 0 LDFLAGS)
           list(GET CONFIG_OUTPUT 1 LIBLIST)
           set(LLVM_XRAY_LDFLAGS ${LDFLAGS} CACHE STRING "Linker flags for LLVMXRay library")
           set(LLVM_XRAY_LIBLIST ${LIBLIST} CACHE STRING "Library list for LLVMXRay")
           set(COMPILER_RT_HAS_LLVMXRAY TRUE)
         endif()
+      endif()
 
-    set(COMPILER_RT_HAS_LLVMTESTINGSUPPORT FALSE)
+      list(FIND CONFIG_OUTPUT testingsupport FOUND_TESTINGSUPPORT)
+      if (NOT FOUND_TESTINGSUPPORT EQUAL -1)
         execute_process(
           COMMAND ${LLVM_CONFIG_PATH} "--ldflags" "--libs" "testingsupport"
           RESULT_VARIABLE HAD_ERROR
           OUTPUT_VARIABLE CONFIG_OUTPUT
           ERROR_QUIET)
         if (HAD_ERROR)
           message(WARNING "llvm-config finding testingsupport failed with status ${HAD_ERROR}")
         else()
           string(REGEX REPLACE "[ \t]*[\r\n]+[ \t]*" ";" CONFIG_OUTPUT ${CONFIG_OUTPUT})
           list(GET CONFIG_OUTPUT 0 LDFLAGS)
           list(GET CONFIG_OUTPUT 1 LIBLIST)
           if (LIBLIST STREQUAL "")
             message(WARNING "testingsupport library not installed, some tests will be skipped")
           else()
             set(LLVM_TESTINGSUPPORT_LDFLAGS ${LDFLAGS} CACHE STRING "Linker flags for LLVMTestingSupport library")
             set(LLVM_TESTINGSUPPORT_LIBLIST ${LIBLIST} CACHE STRING "Library list for LLVMTestingSupport")
             set(COMPILER_RT_HAS_LLVMTESTINGSUPPORT TRUE)
           endif()
         endif()
+      endif()
+    endif()
 
     # Make use of LLVM CMake modules.
     # --cmakedir is supported since llvm r291218 (4.0 release)
     execute_process(
       COMMAND ${LLVM_CONFIG_PATH} --cmakedir
       RESULT_VARIABLE HAD_ERROR
       OUTPUT_VARIABLE CONFIG_OUTPUT)
     if(NOT HAD_ERROR)