curl-wolfssl.m4: error out if wolfSSL is not usable

When I explicitly declare, that I would like to have curl built with
wolfSSL support using `--with-wolfssl` configure option, then I would
expect, that either I endup with curl having that support, for example
in form of https support or it wouldn't be available at all.

Downstream projects like for example OpenWrt build curl wolfSSL variant
with `--with-wolfssl` already, but in certain corner cases it does fail:

  configure:25299: checking for wolfSSL_Init in -lwolfssl
  configure:25321: x86_64-openwrt-linux-musl-gcc -o conftest [snip]
  In file included from target-x86_64_musl/usr/include/wolfssl/wolfcrypt/dsa.h:33,
                   from target-x86_64_musl/usr/include/wolfssl/wolfcrypt/asn_public.h:35,
                  from target-x86_64_musl/usr/include/wolfssl/ssl.h:35,
                   from conftest.c:47:
  target-x86_64_musl/usr/include/wolfssl/wolfcrypt/integer.h:37:14: fatal error: wolfssl/wolfcrypt/sp_int.h: No such file or directory
       #include <wolfssl/wolfcrypt/sp_int.h>
                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
  compilation terminated.

and in the end thus produces curl without https support:

 curl: (1) Protocol "https" not supported or disabled in libcurl

So fix it, by making the working wolfSSL mandatory and error out in
configure step when that's not the case:

 checking for wolfSSL_Init in -lwolfssl... no
 configure: error: --with-wolfssl but wolfSSL was not found or doesn't work

References: https://github.com/openwrt/packages/issues/19005
References: https://github.com/openwrt/packages/issues/19547
Signed-off-by: Petr Štetiar <ynezz@true.cz>

Closes #9682

m4/curl-wolfssl.m4

@@ -154,7 +154,8 @@ if test "x$OPT_WOLFSSL" != xno; then
           AC_MSG_NOTICE([Added $wolfssllibpath to CURL_LIBRARY_PATH])
         fi
       fi
-
+    else
+        AC_MSG_ERROR([--with-wolfssl but wolfSSL was not found or doesn't work])
     fi
 
   fi dnl wolfSSL not disabled