[libc++] Future-proof generate_feature_test_macro_components.py against long names

[• Quuxplusone]

Summary

The proposed-for-C++2b __cpp_lib_default_template_type_for_algorithm_values is 52 characters long, which is enough to reduce the multiplier to less-than-zero, producing an empty string between the name of the macro and its numeric value. Ensure there's always a space between the name of the macro and its value.

When run, this produces no diffs in the generated headers/tests.

libcxx/utils/generate_feature_test_macro_components.py

def get_std_number(std):
     return std.replace('c++', '')
 
 """
   Functions to produce the <version> header
 """
 
 def produce_macros_definition_for_std(std):
   result = ""
-  indent = 56
+  indent = 55
   for tc in feature_test_macros:
     if std not in tc["values"]:
       continue
     inner_indent = 1
     if 'depends' in tc.keys():
       assert 'internal_depends' in tc.keys()
       result += "# if %s\n" % tc["internal_depends"]
       inner_indent += 2
     if get_value_before(tc["values"], std) is not None:
       assert 'depends' not in tc.keys()
       result += "# undef  %s\n" % tc["name"]
     line = "#%sdefine %s" % ((" " * inner_indent), tc["name"])
     line += " " * (indent - len(line))
-    line += "%sL" % tc["values"][std]
+    line += " %sL" % tc["values"][std]
     if 'unimplemented' in tc.keys():
       line = "// " + line
     result += line
     result += "\n"
     if 'depends' in tc.keys():
       result += "# endif\n"
   return result.strip()