[cmake] pass GO_EXECUTABLE to llgo-go

[axw]

Summary

When calling llgo-go from the llvm_add_go_executable
cmake function, specify $GO_EXECUTABLE as the go
command to call. Without this, llgo-go searches $PATH
which may be inconsistent with $GO_EXECUTABLE.

[pcc]

LGTM

cmake/modules/AddLLVM.cmake

if(LLVM_BINDINGS MATCHES "go")
     set(cxx "${CMAKE_CXX_COMPILER} ${CMAKE_CXX_COMPILER_ARG1}")
     set(cppflags "")
     get_property(include_dirs DIRECTORY PROPERTY INCLUDE_DIRECTORIES)
     foreach(d ${include_dirs})
       set(cppflags "${cppflags} -I${d}")
     endforeach(d)
     set(ldflags "${CMAKE_EXE_LINKER_FLAGS}")
     add_custom_command(OUTPUT ${binpath}
-      COMMAND ${CMAKE_BINARY_DIR}/bin/llvm-go "cc=${cc}" "cxx=${cxx}" "cppflags=${cppflags}" "ldflags=${ldflags}"
+      COMMAND ${CMAKE_BINARY_DIR}/bin/llvm-go "go=${GO_EXECUTABLE}" "cc=${cc}" "cxx=${cxx}" "cppflags=${cppflags}" "ldflags=${ldflags}"
               ${ARG_GOFLAGS} build -o ${binpath} ${pkgpath}
       DEPENDS llvm-config ${CMAKE_BINARY_DIR}/bin/llvm-go${CMAKE_EXECUTABLE_SUFFIX}
               ${llvmlibs} ${ARG_DEPENDS}
       COMMENT "Building Go executable ${binary}"
       VERBATIM)
     if (ARG_ALL)
       add_custom_target(${binary} ALL DEPENDS ${binpath})
     else()