build: syms: add support for Mach-O binaries

Current code stolen from waf's extras, only supported 'pe' and 'elf'. OS X
uses the 'Mach-O' binary format (which waf calls 'mac-o'... go figure).

Add support for generating the global symbols file with nm and using it from
clang.

waftools/syms.py

@@ -35,7 +35,7 @@ def run(self):
 				kw['env'] = env
 
 		else:
-			if self.env.DEST_BINFMT == 'pe': #gcc uses nm, and has a preceding _ on windows
+			if self.env.DEST_BINFMT in ('pe', 'mac-o'): #gcc uses nm, and has a preceding _ on windows and osx
 				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')
@@ -56,6 +56,8 @@ def run(self):
 			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")
+		elif self.env.DEST_BINFMT == 'mac-o':
+			self.outputs[0].write('\n'.join("_"+sym for sym in lsyms))
 		else:
 			raise WafError('NotImplemented')
 
@@ -76,6 +78,8 @@ def do_the_symbol_stuff(self):
 		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()])
+	elif self.env.DEST_BINFMT == 'mac-o':
+		self.link_task.env.append_value('LINKFLAGS', ['-exported_symbols_list', tsk.outputs[0].bldpath()])
 	else:
 		raise WafError('NotImplemented')