[gn build] Fix cosmetic bug in write_cmake_config.py

[thakis]

Summary

Before,#cmakedefine FOO resulted in #define FOO with a trailing space if FOO was set to something truthy. Make it so that it's just #define FOO without a trailing space.

No functional difference.

[phosek]

LGTM

llvm/utils/gn/build/write_cmake_config.py

for in_line in in_lines:
         if in_line.startswith('#cmakedefine01 '):
             _, var = in_line.split()
             in_line = '#define %s %d\n' % (var, 1 if values[var] else 0)
             unused_values.discard(var)
         elif in_line.startswith('#cmakedefine '):
             _, var = in_line.split(None, 1)
             try:
                 var, val = var.split(None, 1)
+                in_line = '#define %s %s' % (var, val)  # val ends in \n.
             except:
-                var, val = var.rstrip(), '\n'
-            if values[var]:
-                in_line = '#define %s %s' % (var, val)
-            else:
+                var = var.rstrip()
+                in_line = '#define %s\n' % var
+            if not values[var]:
                 in_line = '/* #undef %s */\n' % var
             unused_values.discard(var)
         out_lines.append(in_line)
 
     if unused_values:
         print >>sys.stderr, 'Unused --values args:'
         print >>sys.stderr, '    ', '\n    '.join(unused_values)
         return 1