Check for OpenSSL functions in headers

[XrXr]

While building with a custom build of OpenSSL, I noticed in mkmf.log
that all the feature detection checks are done using a program lacking
an OpenSSL header include. mkmf retries using a fallback program when
this fails, but that means all the have_func calls compile twice when
compiling once should suffice. Example log without this commit:

have_func: checking for X509_STORE_CTX_get0_cert()... -------------------- yes

DYLD_FALLBACK_LIBRARY_PATH=.:../.. "clang -o conftest ...
conftest.c:14:57: error: use of undeclared identifier 'X509_STORE_CTX_get0_cert'
int t(void) { void ((*volatile p)()); p = (void ((*)()))X509_STORE_CTX_get0_cert; return !p; }
                                                        ^
1 error generated.
checked program was:
/* begin */
 1: #include "ruby.h"
 2:
 3: /*top*/
 4: extern int t(void);
 5: int main(int argc, char **argv)
 6: {
 7:   if (argc > 1000000) {
 8:     int (* volatile tp)(void)=(int (*)(void))&t;
 9:     printf("%d", (*tp)());
10:   }
11:
12:   return !!argv[argc];
13: }
14: int t(void) { void ((*volatile p)()); p = (void ((*)()))X509_STORE_CTX_get0_cert; return !p; }
/* end */

DYLD_FALLBACK_LIBRARY_PATH=.:../.. "clang -o conftest ...
checked program was:
/* begin */
 1: #include "ruby.h"
 2:
 3: /*top*/
 4: extern int t(void);
 5: int main(int argc, char **argv)
 6: {
 7:   if (argc > 1000000) {
 8:     int (* volatile tp)(void)=(int (*)(void))&t;
 9:     printf("%d", (*tp)());
10:   }
11:
12:   return !!argv[argc];
13: }
14: extern void X509_STORE_CTX_get0_cert();
15: int t(void) { X509_STORE_CTX_get0_cert(); return 0; }
/* end */

The second compilation succeeds.

Specify the header for each checked function.

[XrXr]

This change revealed that X509_STORE_get_ex_new_index is a macro, so have_func() should never be able to find it.

conftest.c:16:41: error: too few arguments provided to function-like macro invocation
extern void X509_STORE_get_ex_new_index();
                                        ^
/Users/a/openssl-1.1.1p/prefix/include/openssl/x509_vfy.h:330:9: note: macro 'X509_STORE_get_ex_new_index' defined here
#define X509_STORE_get_ex_new_index(l, p, newf, dupf, freef) \
        ^
conftest.c:17:43: error: too few arguments provided to function-like macro invocation
int t(void) { X509_STORE_get_ex_new_index(); return 0; }
                                          ^
/Users/a/openssl-1.1.1p/prefix/include/openssl/x509_vfy.h:330:9: note: macro 'X509_STORE_get_ex_new_index' defined here
#define X509_STORE_get_ex_new_index(l, p, newf, dupf, freef) \
        ^

From https://www.openssl.org/docs/man1.1.1/man3/X509_STORE_get_ex_new_index.html:

TYPE_get_ex_new_index() is a macro that calls CRYPTO_get_ex_new_index() with the correct index value.

[nobu]

https://github.com/nobu/openssl/runs/7264339285?check_suite_focus=true#step:5:56
You can pass matching arguments to pass a macro too.

[nobu]

But not so significant speed gain as I expected, unfortunately. 😢

[rhenium]

Looks good to me. Thanks!

[rhenium]

Now that LibreSSL supports most of the OpenSSL 1.1 functions, I wonder if we can simply replace all those # added in 1.1.0 entries with OPENSSL_VERSION_NUMBER check. OpenSSL 1.0.2 is the only version that needs it.

It could further cut extconf.rb in half.