Matt noticed errors when running ./configure on dash:
    ./configure: 5339: test: x: unexpected operator
    ./configure: 5386: test: x: unexpected operator

The change is to use POSIX '=' comparison instead of bash-specific ==.

Patch-by: Matt Whitlock
https://bugs.gentoo.org/779187
--- a/configure.ac	2021-03-27 18:25:24.000000000 +0000
+++ b/configure.ac	2021-03-30 01:34:01.993467424 +0000
@@ -65,7 +65,7 @@
 # --enable-benchmarks
 AC_ARG_ENABLE([benchmarks], [AS_HELP_STRING([--enable-benchmarks],
     [build benchmarks])])
-AM_CONDITIONAL([WITH_BENCHMARKS], [test "x$enable_benchmarks" == "xyes"])
+AM_CONDITIONAL([WITH_BENCHMARKS], [test "x$enable_benchmarks" = "xyes"])
 AM_COND_IF([WITH_BENCHMARKS], [
     AC_LANG_PUSH([C++])
     AC_CHECK_HEADERS([benchmark/benchmark.h], [],
@@ -79,7 +79,7 @@
     [AS_HELP_STRING([--enable-benchmarks-regenerate],
     [regenerate C code for benchmarks])])
 AM_CONDITIONAL([REGEN_BENCHMARKS],
-    [test "x$enable_benchmarks_regenerate" == "xyes"])
+    [test "x$enable_benchmarks_regenerate" = "xyes"])
 
 
 # checks for programs
--- a/configure
+++ b/configure
@@ -5336,7 +5336,7 @@ if test "${enable_benchmarks+set}" = set; then :
   enableval=$enable_benchmarks;
 fi
 
- if test "x$enable_benchmarks" == "xyes"; then
+ if test "x$enable_benchmarks" = "xyes"; then
   WITH_BENCHMARKS_TRUE=
   WITH_BENCHMARKS_FALSE='#'
 else
@@ -5383,7 +5383,7 @@ if test "${enable_benchmarks_regenerate+set}" = set; then :
   enableval=$enable_benchmarks_regenerate;
 fi
 
- if test "x$enable_benchmarks_regenerate" == "xyes"; then
+ if test "x$enable_benchmarks_regenerate" = "xyes"; then
   REGEN_BENCHMARKS_TRUE=
   REGEN_BENCHMARKS_FALSE='#'
 else