error: '__s1_len' undeclared (first use in this function)

I'm trying to compile a really old version of PHP and am getting this error:

/tmp/php-5.0.5/ext/openssl/openssl.c:3198:11: error: expected ';' before '__s1_len'
/tmp/php-5.0.5/ext/openssl/openssl.c:3198:11: error: '__s1_len' undeclared (first use in this function)
/tmp/php-5.0.5/ext/openssl/openssl.c:3198:11: error: '__s2_len' undeclared (first use in this function)
/tmp/php-5.0.5/ext/openssl/openssl.c:3198:11: error: expected expression before 'const'
/tmp/php-5.0.5/ext/openssl/openssl.c:3198:11: error: expected expression before 'const'
/tmp/php-5.0.5/ext/openssl/openssl.c:3198:11: error: expected expression before 'const'
/tmp/php-5.0.5/ext/openssl/openssl.c:3198:11: error: expected expression before 'const'
/tmp/php-5.0.5/ext/openssl/openssl.c:3198:11: error: expected expression before 'const'
/tmp/php-5.0.5/ext/openssl/openssl.c:3198:11: error: expected expression before 'const'
/tmp/php-5.0.5/ext/openssl/openssl.c:3198:11: error: expected expression before 'const'
/tmp/php-5.0.5/ext/openssl/openssl.c:3198:11: error: expected expression before 'const'
/tmp/php-5.0.5/ext/openssl/openssl.c:3198:11: error: expected expression before 'const'
/tmp/php-5.0.5/ext/openssl/openssl.c:3198:11: error: expected expression before 'const'
/tmp/php-5.0.5/ext/openssl/openssl.c:3198:11: error: expected expression before 'const'
/tmp/php-5.0.5/ext/openssl/openssl.c:3198:11: error: expected expression before 'const'

Here's line 3198:

match = strcmp(cnmatch, buf) == 0;

That line looks fine to me? I'm also not seeing __s1_len anywhere in the file. Not on line 3198 or on any other line for that matter.

Any ideas?