ext/curl/config.m4: include string.h for test using strncmp()

[orlitzky]

2ecafd41ba updates one of the curl ./configure tests to use strncmp(), but that function may not be defined unless string.h is included. We add it here.

[orlitzky]

cc @bukka

[Sjord]

    if (sscanf(ptr, "OpenSSL/%d.%d", &major, &minor) == 2) {
      /* Check for 1.1.1+ (including 1.1.1a, 1.1.1b, etc.) */
      if ((major > 1) || (major == 1 && minor == 1 && strncmp(ptr + 12, "1", 1) == 0)) {

ptr contains OpenSSL/1.1.1. sscanf checks the first part and strncmp checks the last number. I think this is not so elegant. Isn't it easier to parse OpenSSL/%d.%d.%d so that you have the three numbers?

strncmp(ptr + 12, "1", 1)

Couldn't this just be ptr[12] == '1'?

What happens if ptr does not contain 12 characters?

[orlitzky]

What happens if ptr does not contain 12 characters?

The test could be improved, but it's looking for very old versions of OpenSSL, so it may need someone on an LTS distro to experiment/debug.

Worst case, the test program segfaults and the ./configure test fails.

[orlitzky]

This isn't a huge problem since the test is checking for an unsuitable version of OpenSSL (i.e. all errors are success), but it's a time bomb that may go off if the check is ever refactored @petk

[orlitzky]

Thank you!