Use execvp rather then execv in exec_process (#22737)

When this code was added in #20909 it broke users who were doing
`EM_COMPILER_WRAPPER=cache` since it was not using PATH to find the
executable (unlike the subprocess module).

Fixes: #22736

Author: sbc100

.circleci/config.yml

@@ -787,7 +787,7 @@ jobs:
       EMTEST_SKIP_NODE_CANARY: "1"
       EMTEST_SKIP_WASM64: "1"
     steps:
-      - run: apt-get install -q -y ninja-build scons
+      - run: apt-get install -q -y ninja-build scons ccache
       - run-tests-linux:
           # some native-dependent tests fail because of the lack of native
           # headers on emsdk-bundled clang

test/test_other.py

@@ -154,6 +154,18 @@ def decorated(self, *args, **kwargs):
   return decorated
 
 
+def requires_ccache(func):
+  assert callable(func)
+
+  @wraps(func)
+  def decorated(self, *args, **kwargs):
+    if not shutil.which('ccache'):
+      self.fail('test requires ccache to be installed (available in PATH)')
+    return func(self, *args, **kwargs)
+
+  return decorated
+
+
 def requires_scons(func):
   assert callable(func)
 
@@ -12554,6 +12566,11 @@ def test_compiler_wrapper(self):
     self.assertContained('wrapping compiler call: ', stdout)
     self.assertExists('test_hello_world.o')
 
+  @requires_ccache
+  @with_env_modify({'EM_COMPILER_WRAPPER': 'ccache'})
+  def test_compiler_wrapper_ccache(self):
+    self.do_runf('hello_world.c', 'hello, world!')
+
   def test_llvm_option_dash_o(self):
     # emcc used to interpret -mllvm's option value as the output file if it
     # began with -o

tools/shared.py

@@ -249,7 +249,7 @@ def exec_process(cmd):
   else:
     sys.stdout.flush()
     sys.stderr.flush()
-    os.execv(cmd[0], cmd)
+    os.execvp(cmd[0], cmd)
 
 
 def run_js_tool(filename, jsargs=[], node_args=[], **kw):  # noqa: mutable default args