Doh! In include/bits/uClibc_config.h when we define things, we appropriately

prepend "__".  Unfortunately, when we #undef things, we do not prepend the
"__".  This results in collateral damage to unsuspecting applications as we
undefine random unrelated macros.  Oops.

For example, when compiling xfree86, libGLcore.a defines MALLOC for its own usage.
But include/bits/uClibc_config.h then does an
    #undef MALLOC
    #define __MALLOC_930716__ 1
which inadvertantly trashes the define from libGLcore....  Ouch.

The autogenerated include/bits/uClibc_config.h should instead have
contained:
    #undef __MALLOC__
    #define __MALLOC_930716__ 1

This patch makes that happen.

extra/config/confdata.c

@@ -347,7 +347,7 @@ int conf_write(const char *name)
 				case no:
 					fprintf(out, "# %s is not set\n", sym->name);
 					if (out_h)
-						fprintf(out_h, "#undef %s\n", sym->name);
+						fprintf(out_h, "#undef __%s__\n", sym->name);
 					break;
 				case mod:
 					fprintf(out, "%s=m\n", sym->name);