build: include a copy of syms.py from upstream waf

The alternatives to copying this small bit of code are even worse.

This is unmodified, except for the added line 3.

waftools/syms.py

@@ -0,0 +1,81 @@
+#! /usr/bin/env python
+# encoding: utf-8
+# Source: waflib/extras/syms.py from waf git 610d0d59f (New BSD License)
+
+"""
+this tool supports the export_symbols_regex to export the symbols in a shared library.
+by default, all symbols are exported by gcc, and nothing by msvc.
+to use the tool, do something like:
+
+def build(ctx):
+	ctx(features='c cshlib syms', source='a.c b.c', export_symbols_regex='mylib_.*', target='testlib')
+
+only the symbols starting with 'mylib_' will be exported.
+"""
+
+import os
+import re
+from waflib.Context import STDOUT
+from waflib.Task import Task
+from waflib.Errors import WafError
+from waflib.TaskGen import feature, after_method
+
+class gen_sym(Task):
+	def run(self):
+		obj = self.inputs[0]
+		kw = {}
+		if 'msvc' in (self.env.CC_NAME, self.env.CXX_NAME):
+			re_nm = re.compile(r'External\s+\|\s+_(' + self.generator.export_symbols_regex + r')\b')
+			cmd = [self.env.DUMPBIN or 'dumpbin', '/symbols', obj.abspath()]
+
+			# Dumpbin requires custom environment sniffed out by msvc.py earlier
+			if self.env['PATH']:
+				env = dict(self.env.env or os.environ)
+				env.update(PATH = os.pathsep.join(self.env['PATH']))
+				kw['env'] = env
+
+		else:
+			if self.env.DEST_BINFMT == 'pe': #gcc uses nm, and has a preceding _ on windows
+				re_nm = re.compile(r'T\s+_(' + self.generator.export_symbols_regex + r')\b')
+			else:
+				re_nm = re.compile(r'T\s+(' + self.generator.export_symbols_regex + r')\b')
+			cmd = [self.env.NM or 'nm', '-g', obj.abspath()]
+		syms = re_nm.findall(self.generator.bld.cmd_and_log(cmd, quiet=STDOUT, **kw))
+		self.outputs[0].write('%r' % syms)
+
+class compile_sym(Task):
+	def run(self):
+		syms = {}
+		for x in self.inputs:
+			slist = eval(x.read())
+			for s in slist:
+				syms[s] = 1
+		lsyms = list(syms.keys())
+		lsyms.sort()
+		if self.env.DEST_BINFMT == 'pe':
+			self.outputs[0].write('EXPORTS\n' + '\n'.join(lsyms))
+		elif self.env.DEST_BINFMT == 'elf':
+			self.outputs[0].write('{ global:\n' + ';\n'.join(lsyms) + ";\nlocal: *; };\n")
+		else:
+			raise WafError('NotImplemented')
+
+@feature('syms')
+@after_method('process_source', 'process_use', 'apply_link', 'process_uselib_local')
+def do_the_symbol_stuff(self):
+	ins = [x.outputs[0] for x in self.compiled_tasks]
+	self.gen_sym_tasks = [self.create_task('gen_sym', x, x.change_ext('.%d.sym' % self.idx)) for x in ins]
+
+	tsk = self.create_task('compile_sym',
+			       [x.outputs[0] for x in self.gen_sym_tasks],
+			       self.path.find_or_declare(getattr(self, 'sym_filename', self.target + '.def')))
+	self.link_task.set_run_after(tsk)
+	self.link_task.dep_nodes.append(tsk.outputs[0])
+	if 'msvc' in (self.env.CC_NAME, self.env.CXX_NAME):
+		self.link_task.env.append_value('LINKFLAGS', ['/def:' + tsk.outputs[0].bldpath()])
+	elif self.env.DEST_BINFMT == 'pe': #gcc on windows takes *.def as an additional input
+		self.link_task.inputs.append(tsk.outputs[0])
+	elif self.env.DEST_BINFMT == 'elf':
+		self.link_task.env.append_value('LINKFLAGS', ['-Wl,-version-script', '-Wl,' + tsk.outputs[0].bldpath()])
+	else:
+		raise WafError('NotImplemented')
+