autotools: confirm openssl is working before using

latest versions of macOS provide pkg-config and libraries for an ancient
version of openssl as part of the system, but no headers

diff --git a/m4/libevent_openssl.m4 b/m4/libevent_openssl.m4
index c20405950319e73ebe4367e7f3817b4e66178720..7b4581340552cc56fae16e482478145b0b5ff977 100644 (file)
--- a/m4/libevent_openssl.m4
+++ b/m4/libevent_openssl.m4
@@ -39,6 +39,10 @@ case "$enable_openssl" in
        done
        ;;
     esac
+    CPPFLAGS_SAVE=$CPPFLAGS
+    CPPFLAGS+=$OPENSSL_INCS
+    AC_CHECK_HEADERS([openssl/ssl.h], [], [have_openssl=no])
+    CPPFLAGS=$CPPFLAGS_SAVE
     AC_SUBST(OPENSSL_INCS)
     AC_SUBST(OPENSSL_LIBS)
     case "$have_openssl" in