[pseudo] Fix pseudo-gen usage when cross-compiling

Use the LLVM build system's cross-compilation support for the tool, so
that the build works for both host and cross-compilation scenarios.

Reviewed By: sammccall

Differential Revision: https://reviews.llvm.org/D126397

Author: smeenai

clang-tools-extra/pseudo/include/CMakeLists.txt

@@ -1,25 +1,35 @@
 # The cxx.bnf grammar file
 set(cxx_bnf ${CMAKE_CURRENT_SOURCE_DIR}/../lib/cxx.bnf)
 
+# Using CMAKE_CROSSCOMPILING and not LLVM_USE_HOST_TOOLS because the latter is
+# also set for LLVM_OPTIMIZED_TABLEGEN, which we don't care about here.
+if(CMAKE_CROSSCOMPILING)
+  build_native_tool(pseudo-gen pseudo_gen)
+  set(pseudo_gen_target "${pseudo_gen}")
+else()
+  set(pseudo_gen $<TARGET_FILE:pseudo-gen>)
+  set(pseudo_gen_target pseudo-gen)
+endif()
+
 # Generate inc files.
 set(cxx_symbols_inc ${CMAKE_CURRENT_BINARY_DIR}/CXXSymbols.inc)
 add_custom_command(OUTPUT ${cxx_symbols_inc}
-   COMMAND "${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/pseudo-gen"
+   COMMAND "${pseudo_gen}"
      --grammar ${cxx_bnf}
      --emit-symbol-list
      -o ${cxx_symbols_inc}
    COMMENT "Generating nonterminal symbol file for cxx grammar..."
-   DEPENDS pseudo-gen
+   DEPENDS ${pseudo_gen_target}
    VERBATIM)
 
 set(cxx_bnf_inc ${CMAKE_CURRENT_BINARY_DIR}/CXXBNF.inc)
 add_custom_command(OUTPUT ${cxx_bnf_inc}
-   COMMAND "${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/pseudo-gen"
+   COMMAND "${pseudo_gen}"
      --grammar ${cxx_bnf}
      --emit-grammar-content
      -o ${cxx_bnf_inc}
    COMMENT "Generating bnf string file for cxx grammar..."
-   DEPENDS pseudo-gen
+   DEPENDS ${pseudo_gen_target}
    VERBATIM)
 
 # add_custom_command does not create a new target, we need to deine a target