configure: add basic test of --with-ssl prefix

When given a prefix, the $PREFIX_OPENSSL/lib/openssl.pc or
$PREFIX_OPENSSL/include/openssl/ssl.h files must be present or cause an
error. Helps users detect when giving configure the wrong path.

Reported-by: Oleg Pudeyev
Assisted-by: Per Malmberg
Fixes #2580

diff --git a/configure.ac b/configure.ac
index 24e47aa33a5ba632b3b535b944e8e6bde5d5ce8e..c552c46ab32e4bdde4a9bcc2da6477dff0198bb9 100755 (executable)
--- a/configure.ac
+++ b/configure.ac
@@ -1591,9 +1591,11 @@ if test -z "$ssl_backends" -o "x$OPT_SSL" != xno &&
     dnl specify PKG_CONFIG_LIBDIR we're only looking where
     dnl the user told us to look
     OPENSSL_PCDIR="$OPT_SSL/lib/pkgconfig"
-    AC_MSG_NOTICE([PKG_CONFIG_LIBDIR will be set to "$OPENSSL_PCDIR"])
     if test -f "$OPENSSL_PCDIR/openssl.pc"; then
+      AC_MSG_NOTICE([PKG_CONFIG_LIBDIR will be set to "$OPENSSL_PCDIR"])
       PKGTEST="yes"
+    elif test ! -f "$PREFIX_OPENSSL/include/openssl/ssl.h"; then
+      AC_MSG_ERROR([$PREFIX_OPENSSL is a bad --with-ssl prefix!])
     fi
 
     dnl in case pkg-config comes up empty, use what we got