[CMake] Use llvm-tblgen from NATIVE LLVM build when cross-compiling

[xiaobai]

Summary

When cross-compiling LLDB, we want to use llvm-tblgen built for the
host, not the target.

[compnerd]

cmake/modules/LLDBStandalone.cmake

44

Please add a comment that this will always be built release and thus we can assume that directory structure.

[xiaobai]

Added a comment

cmake/modules/LLDBStandalone.cmake

if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
   set(LLVM_CMAKE_PATH ${LLVM_CMAKE_DIR} CACHE PATH "Path to LLVM CMake modules")
 
   set(LLVM_MAIN_SRC_DIR ${LLVM_BUILD_MAIN_SRC_DIR} CACHE PATH "Path to LLVM source tree")
   set(LLVM_MAIN_INCLUDE_DIR ${LLVM_BUILD_MAIN_INCLUDE_DIR} CACHE PATH "Path to llvm/include")
   set(LLVM_LIBRARY_DIR ${LLVM_BUILD_LIBRARY_DIR} CACHE PATH "Path to llvm/lib")
   set(LLVM_BINARY_DIR ${LLVM_BUILD_BINARY_DIR} CACHE PATH "Path to LLVM build tree")
   set(LLVM_EXTERNAL_LIT ${LLVM_TOOLS_BINARY_DIR}/llvm-lit CACHE PATH "Path to llvm-lit")
 
+  if(CMAKE_CROSSCOMPILING)
+    set(LLVM_NATIVE_BUILD "${LLDB_PATH_TO_LLVM_BUILD}/NATIVE")
+    if (NOT EXISTS "${LLVM_NATIVE_BUILD}")
+      message(FATAL_ERROR
+        "Attempting to cross-compile LLDB standalone but no native LLVM build
+        found. Please cross-compile LLVM as well.")
+    endif()
+
+    if (CMAKE_HOST_SYSTEM_NAME MATCHES "Windows")
+      set(HOST_EXECUTABLE_SUFFIX ".exe")
+    endif()
+
+    if (NOT CMAKE_CONFIGURATION_TYPES)
+      set(LLVM_TABLEGEN_EXE
+        "${LLVM_NATIVE_BUILD}/bin/llvm-tblgen${HOST_EXECUTABLE_SUFFIX}")
+    else()
+      # NOTE: LLVM NATIVE build is always built Release, as is specified in
+      # CrossCompile.cmake
+      set(LLVM_TABLEGEN_EXE
+        "${LLVM_NATIVE_BUILD}/Release/bin/llvm-tblgen${HOST_EXECUTABLE_SUFFIX}")
+    endif()
+  else()
     find_program(LLVM_TABLEGEN_EXE "llvm-tblgen" ${LLVM_TOOLS_BINARY_DIR}
       NO_DEFAULT_PATH)
+  endif()
 
   # They are used as destination of target generators.
   set(LLVM_RUNTIME_OUTPUT_INTDIR ${CMAKE_BINARY_DIR}/${CMAKE_CFG_INTDIR}/bin)
   set(LLVM_LIBRARY_OUTPUT_INTDIR ${CMAKE_BINARY_DIR}/${CMAKE_CFG_INTDIR}/lib${LLVM_LIBDIR_SUFFIX})
   if(WIN32 OR CYGWIN)
     # DLL platform -- put DLLs into bin.
     set(LLVM_SHLIB_OUTPUT_INTDIR ${LLVM_RUNTIME_OUTPUT_INTDIR})
   else()