[flang] Fix bug in tests for standalone build

[tskeith]

Summary

When doing a standalone build of flang against an LLVM that contains a
built flang, the tests were run on the flang from LLVM rather than on
the one that was just built.

The problem was in the lit configuration for finding %flang etc.
Fix it to look only in the directory where it was built.

flang/test/lit.cfg.py

 if config.flang_llvm_tools_dir != "" :
   config.available_features.add('fir')
   if config.llvm_tools_dir != config.flang_llvm_tools_dir :
     llvm_config.with_environment('PATH', config.flang_llvm_tools_dir, append_path=True)
 
 config.substitutions.append(('%B', config.flang_obj_root))
 
 # For each occurrence of a flang tool name, replace it with the full path to
-# the build directory holding that tool.  We explicitly specify the directories
-# to search to ensure that we get the tools just built and not some random
-# tools that might happen to be in the user's PATH.
-tool_dirs = [config.llvm_tools_dir, config.flang_tools_dir]
-flang_includes = "-I" + config.flang_intrinsic_modules_dir
-
-tools = [ToolSubst('%flang', command=FindTool('flang'), unresolved='fatal'),
-         ToolSubst('%f18', command=FindTool('f18'), unresolved='fatal'),
-         ToolSubst('%f18_with_includes', command=FindTool('f18'),
-         extra_args=[flang_includes], unresolved='fatal')]
-
-llvm_config.add_tool_substitutions(tools, tool_dirs)
+# the build directory holding that tool.
+tools = [
+  ToolSubst('%flang', command=FindTool('flang'), unresolved='fatal'),
+    extra_args=["-I" + config.flang_intrinsic_modules_dir], unresolved='fatal')
+]
+llvm_config.add_tool_substitutions(tools, [config.flang_llvm_tools_dir])
 
 # Enable libpgmath testing
 result = lit_config.params.get("LIBPGMATH")
 if result:
     config.environment["LIBPGMATH"] = True

flang/test/lit.site.cfg.py.in

 @LIT_SITE_CFG_IN_HEADER@
 
 import sys
 
 config.llvm_tools_dir = "@LLVM_TOOLS_DIR@"
 config.flang_obj_root = "@FLANG_BINARY_DIR@"
 config.flang_src_dir = "@FLANG_SOURCE_DIR@"
 config.flang_tools_dir = "@FLANG_TOOLS_DIR@"
 config.flang_intrinsic_modules_dir = "@FLANG_INTRINSIC_MODULES_DIR@"
-config.flang_llvm_tools_dir = "@LLVM_RUNTIME_OUTPUT_INTDIR@"
+config.flang_llvm_tools_dir = "@CMAKE_BINARY_DIR@/bin"
 config.python_executable = "@PYTHON_EXECUTABLE@"
 
 # Support substitution of the tools_dir with user parameters. This is
 # used when we can't determine the tool dir at configuration time.
 try:
     config.llvm_tools_dir = config.llvm_tools_dir % lit_config.params
     config.flang_tools_dir = config.flang_tools_dir % lit_config.params
 except KeyError: