$NetBSD$

Remediate bashism.  Reported on mailinglist 20190126.

--- configure.orig	2019-02-16 07:27:13.000000000 +0000
+++ configure
@@ -18983,7 +18983,7 @@ if test "${with_external_gtest+set}" = s
 fi
 
 
-if test "x$with_external_gtest" == "xyes" ; then
+if test "x$with_external_gtest" = "xyes" ; then
     { $as_echo "$as_me:${as_lineno-$LINENO}: result: using external GTest." >&5
 $as_echo "using external GTest." >&6; }
 
@@ -19082,7 +19082,7 @@ $as_echo "using internal GTest." >&6; }
     GTEST_CFLAGS="-I\$(top_srcdir)/test/googletest/include"
     GTEST_LIBS="\$(top_builddir)/test/googletest/libgtest.la"
 fi
- if test "x$with_external_gtest" == "xyes"; then
+ if test "x$with_external_gtest" = "xyes"; then
   USE_EXTERNAL_GTEST_TRUE=
   USE_EXTERNAL_GTEST_FALSE='#'
 else
