Remove unnecessary building.clear function. NFC (#16542)

This function was only called from `tests/test_benchmark.py` and it had
no purpose.  These tests the tests in general (including the
benchmarker) always run emcc as a separate process. Calling this fuction
doesn't effect past of future calls to emcc.

This also allowed me to completely remove the cleanup method from
`tests/test_benchmark.py` since I notices the environment overrides were
already invjected by `env=` paramaeters to the emcc subprocess.  This
meant that overriding the current process environment was not needed.

Author: sbc100

tests/test_benchmark.py

@@ -163,9 +163,6 @@ def get_output_files(self):
   def get_size_text(self):
     return 'dynamically linked - libc etc. are not included!'
 
-  def cleanup(self):
-    pass
-
 
 def run_binaryen_opts(filename, opts):
   run_process([
@@ -181,14 +178,11 @@ def __init__(self, name, engine, extra_args=[], env={}, binaryen_opts=[]):
     self.engine = engine
     self.extra_args = extra_args.copy()
     self.env = os.environ.copy()
-    for k, v in env.items():
-      self.env[k] = v
+    self.env.update(env)
     self.binaryen_opts = binaryen_opts.copy()
 
   def build(self, parent, filename, args, shared_args, emcc_args, native_args, native_exec, lib_builder, has_output_parser):
     self.filename = filename
-    self.old_env = os.environ
-    os.environ = self.env.copy()
     llvm_root = self.env.get('LLVM') or config.LLVM_ROOT
     if lib_builder:
       env_init = self.env.copy()
@@ -240,10 +234,6 @@ def get_output_files(self):
       ret.append(self.filename[:-3] + '.wasm')
     return ret
 
-  def cleanup(self):
-    os.environ = self.old_env
-    building.clear()
-
 
 class EmscriptenWasm2CBenchmarker(EmscriptenBenchmarker):
   def __init__(self, name):
@@ -351,9 +341,6 @@ def run(self, args):
   def get_output_files(self):
     return [self.filename, self.filename.replace('.js', '.wasm')]
 
-  def cleanup(self):
-    pass
-
 
 # Benchmarkers
 
@@ -476,7 +463,6 @@ def do_benchmark(self, name, src, expected_output='FAIL', args=[],
       b.build(self, filename, args, shared_args, emcc_args, native_args, native_exec, lib_builder, has_output_parser=output_parser is not None)
       b.bench(args, output_parser, reps, expected_output)
       b.display(baseline)
-      b.cleanup()
 
   def test_primes(self, check=True):
     src = r'''

tools/building.py

@@ -42,8 +42,6 @@
 EXPECTED_BINARYEN_VERSION = 105
 # cache results of nm - it can be slow to run
 nm_cache = {}
-# Stores the object files contained in different archive files passed as input
-ar_contents = {}
 _is_ar_cache = {}
 # the exports the user requested
 user_requested_exports = set()
@@ -122,15 +120,6 @@ def check(value):
   return [v for v in values if check(v)]
 
 
-# clear caches. this is not normally needed, except if the clang/LLVM
-# used changes inside this invocation of Building, which can happen in the benchmarker
-# when it compares different builds.
-def clear():
-  nm_cache.clear()
-  ar_contents.clear()
-  _is_ar_cache.clear()
-
-
 # .. but for Popen, we cannot have doublequotes, so provide functionality to
 # remove them when needed.
 def remove_quotes(arg):
@@ -208,6 +197,8 @@ def read_link_inputs(files):
   # each of them provides. Do this in multiple parallel processes.
   archive_names = [] # .a files passed in to the command line to the link
   object_names = [] # .o/.bc files passed in to the command line to the link
+  # Stores the object files contained in different archive files passed as input
+  ar_contents = {}
   for f in files:
     absolute_path_f = make_paths_absolute(f)
 
@@ -228,6 +219,7 @@ def read_link_inputs(files):
   # Next, extract symbols from all object files (either standalone or inside archives we just extracted)
   # The results are not used here directly, but populated to llvm-nm cache structure.
   llvm_nm_multiple(object_names)
+  return ar_contents
 
 
 def llvm_backend_args():
@@ -443,6 +435,8 @@ def consider_object(f, force_add=False):
       files_to_link.append(f)
     return do_add
 
+  ar_contents = read_link_inputs(input_files)
+
   # Traverse a single archive. The object files are repeatedly scanned for
   # newly satisfied symbols until no new symbols are found. Returns true if
   # any object files were added to the link.
@@ -465,8 +459,6 @@ def consider_archive(f, force_add):
     logger.debug('done running loop of archive %s' % (f))
     return added_any_objects
 
-  read_link_inputs(input_files)
-
   # Rescan a group of archives until we don't find any more objects to link.
   def scan_archive_group(group):
     loop_again = True