configure: look for libngtcp2_crypto_libressl first

configure only fall back to quictls when libressl crypto was not found

configure.ac

@@ -3241,7 +3241,66 @@ if test X"$want_tcp2" != Xno; then
   fi
 fi
 
-if test "x$USE_NGTCP2" = "x1" -a "x$OPENSSL_ENABLED" = "x1" -a \
+if test "x$USE_NGTCP2" = "x1" -a "x$OPENSSL_ENABLED" = "x1" -a "$HAVE_LIBRESSL" = "1"; then
+  dnl backup the pre-ngtcp2_crypto_libressl variables
+  CLEANLDFLAGS="$LDFLAGS"
+  CLEANLDFLAGSPC="$LDFLAGSPC"
+  CLEANCPPFLAGS="$CPPFLAGS"
+  CLEANLIBS="$LIBS"
+
+  CURL_CHECK_PKGCONFIG(libngtcp2_crypto_libressl, $want_tcp2_path)
+
+  if test "$PKGCONFIG" != "no"; then
+    LIB_NGTCP2_CRYPTO_LIBRESSL=`CURL_EXPORT_PCDIR([$want_tcp2_path])
+      $PKGCONFIG --libs-only-l libngtcp2_crypto_libressl`
+    AC_MSG_NOTICE([-l is $LIB_NGTCP2_CRYPTO_LIBRESSL])
+
+    CPP_NGTCP2_CRYPTO_LIBRESSL=`CURL_EXPORT_PCDIR([$want_tcp2_path]) dnl
+      $PKGCONFIG --cflags-only-I libngtcp2_crypto_libressl`
+    AC_MSG_NOTICE([-I is $CPP_NGTCP2_CRYPTO_LIBRESSL])
+
+    LD_NGTCP2_CRYPTO_LIBRESSL=`CURL_EXPORT_PCDIR([$want_tcp2_path])
+      $PKGCONFIG --libs-only-L libngtcp2_crypto_libressl`
+    AC_MSG_NOTICE([-L is $LD_NGTCP2_CRYPTO_LIBRESSL])
+
+    LDFLAGS="$LDFLAGS $LD_NGTCP2_CRYPTO_LIBRESSL"
+    LDFLAGSPC="$LDFLAGSPC $LD_NGTCP2_CRYPTO_LIBRESSL"
+    CPPFLAGS="$CPPFLAGS $CPP_NGTCP2_CRYPTO_LIBRESSL"
+    LIBS="$LIB_NGTCP2_CRYPTO_LIBRESSL $LIBS"
+
+    if test "x$cross_compiling" != "xyes"; then
+      DIR_NGTCP2_CRYPTO_LIBRESSL=`echo $LD_NGTCP2_CRYPTO_LIBRESSL | $SED -e 's/^-L//'`
+    fi
+    AC_CHECK_LIB(ngtcp2_crypto_libressl, ngtcp2_crypto_recv_client_initial_cb,
+      [
+        AC_CHECK_HEADERS(ngtcp2/ngtcp2_crypto.h,
+          USE_NGTCP2=1
+          CURL_LIBRARY_PATH="$CURL_LIBRARY_PATH:$DIR_NGTCP2_CRYPTO_LIBRESSL"
+          export CURL_LIBRARY_PATH
+          AC_MSG_NOTICE([Added $DIR_NGTCP2_CRYPTO_LIBRESSL to CURL_LIBRARY_PATH])
+          LIBCURL_PC_REQUIRES_PRIVATE="$LIBCURL_PC_REQUIRES_PRIVATE libngtcp2_crypto_libressl"
+        )
+      ],
+        dnl not found, revert back to clean variables
+        LDFLAGS=$CLEANLDFLAGS
+        LDFLAGSPC=$CLEANLDFLAGSPC
+        CPPFLAGS=$CLEANCPPFLAGS
+        LIBS=$CLEANLIBS
+    )
+
+  else
+    dnl no ngtcp2_crypto_libressl pkg-config found, deal with it
+    if test X"$want_tcp2" != Xdefault; then
+      dnl To avoid link errors, we do not allow --with-ngtcp2 without
+      dnl a pkgconfig file
+      AC_MSG_WARN([--with-ngtcp2 was specified but could not find ngtcp2_crypto_libressl pkg-config file.])
+      dnl Pretend to be quictls to fall back to using ngtcp2_crypto_quictls
+    fi
+    HAVE_LIBRESSL=0
+  fi
+fi
+
+if test "x$USE_NGTCP2" = "x1" -a "x$OPENSSL_ENABLED" = "x1" -a "$HAVE_LIBRESSL" != "1" -a \
    "x$OPENSSL_IS_BORINGSSL" != "x1" -a "x$OPENSSL_QUIC_API2" != "x1"; then
   dnl backup the pre-ngtcp2_crypto_quictls variables
   CLEANLDFLAGS="$LDFLAGS"

m4/curl-openssl.m4

@@ -292,6 +292,7 @@ if test "x$OPT_OPENSSL" != xno; then
     ],[
       AC_MSG_RESULT([yes])
       ssl_msg="LibreSSL"
+      HAVE_LIBRESSL=1
     ],[
       AC_MSG_RESULT([no])
     ])