Remove PYTHON key from .emscripten config file.

While reviewing #9166 I noticed that support a PYTHON key in the config
file but this doesn't effect any of the entry point (on UNIX the entry
points are defined by the #! line, on windows they are are defined as
`python` in the bat files.  So really this was only effecting python
sub-processes not the compiler itself.  This feature doesn't seem like
its useful, and also has no tests, so removing it for now.

However for the benefit of #9166 add support for setting this via the
`EM_PYTHON` environment variable.

Author: sbc100

tools/settings_template_readonly.py

@@ -4,8 +4,8 @@
 # Note: If you put paths relative to the home directory, do not forget
 # os.path.expanduser
 
-# Note: On Windows, remember to escape backslashes! I.e. PYTHON='c:\Python27\'
-# is not valid, but PYTHON='c:\\Python27\\' and PYTHON='c:/Python27/'
+# Note: On Windows, remember to escape backslashes! I.e. LLVM='c:\llvm\'
+# is not valid, but LLVM='c:\\llvm\\' and LLVM='c:/llvm/'
 # are.
 
 import os
@@ -17,9 +17,6 @@
 LLVM_ROOT = os.path.expanduser(os.getenv('LLVM', '{{{ LLVM_ROOT }}}')) # directory
 BINARYEN_ROOT = os.path.expanduser(os.getenv('BINARYEN', '')) # if not set, we will use it from ports
 
-# If not specified, defaults to sys.executable.
-# PYTHON = 'python'
-
 # Add this if you have manually built the JS optimizer executable (in
 # Emscripten/tools/optimizer) and want to run it from a custom location.
 # Alternatively, you can set this as the environment variable

tools/shared.py

@@ -281,6 +281,8 @@ def generate_config(path, first_time=False):
     generate_config(EM_CONFIG, first_time=True)
     sys.exit(0)
 
+PYTHON = os.getenv('EM_PYTHON', sys.executable)
+
 # The following globals can be overridden by the config file.
 # See parse_config_file below.
 NODE_JS = None
@@ -295,7 +297,6 @@ def generate_config(path, first_time=False):
 CLOSURE_COMPILER = None
 EMSCRIPTEN_NATIVE_OPTIMIZER = None
 JAVA = None
-PYTHON = None
 JS_ENGINE = None
 JS_ENGINES = []
 COMPILER_OPTS = []
@@ -324,7 +325,6 @@ def parse_config_file():
     'CLANG_ADD_VERSION',
     'CLOSURE_COMPILER',
     'JAVA',
-    'PYTHON',
     'JS_ENGINE',
     'JS_ENGINES',
     'COMPILER_OPTS',
@@ -531,12 +531,6 @@ def perform_sanify_checks():
       if not os.path.exists(cmd) and not os.path.exists(cmd + '.exe'):  # .exe extension required for Windows
         exit_with_error('Cannot find %s, check the paths in %s', cmd, EM_CONFIG)
 
-  if not os.path.exists(PYTHON) and not os.path.exists(cmd + '.exe'):
-    try:
-      run_process([PYTHON, '--xversion'], stdout=PIPE, stderr=PIPE)
-    except (OSError, subprocess.CalledProcessError):
-      exit_with_error('Cannot find %s, check the paths in config file (%s)', PYTHON, CONFIG_FILE)
-
   # Sanity check passed!
   with ToolchainProfiler.profile_block('sanity closure compiler'):
     if not check_closure_compiler():
@@ -916,10 +910,6 @@ def apply_configuration():
 if CLOSURE_COMPILER is None:
   CLOSURE_COMPILER = path_from_root('third_party', 'closure-compiler', 'compiler.jar')
 
-if PYTHON is None:
-  logger.debug('PYTHON not defined in ' + hint_config_file_location() + ', using "%s"' % (sys.executable,))
-  PYTHON = sys.executable
-
 if JAVA is None:
   logger.debug('JAVA not defined in ' + hint_config_file_location() + ', using "java"')
   JAVA = 'java'