build: fix shell == mis-use

The "test" program uses =, not ==.  A lot of shells accept == as an
extension, but not all do and it's technically out of spec.

Signed-off-by: David Lamparter <equinox@diac24.net>

configure.ac

@@ -30,7 +30,7 @@ build_clippy="true"
 
 dnl case 1: external clippy
 if test -n "$with_clippy" -a "$with_clippy" != "no" -a "$with_clippy" != "yes"; then
-  if test "$enable_clippy_only" == "yes"; then
+  if test "$enable_clippy_only" = "yes"; then
     AC_MSG_ERROR([--enable-clippy-only does not make sense with --with-clippy])
   fi
 

m4/ax_python.m4

@@ -186,7 +186,7 @@ AC_REQUIRE([PKG_PROG_PKG_CONFIG])dnl
       AC_MSG_RESULT([yes])
 
       PYTHON_CFLAGS="`\"$pycfg\" --includes`"
-      if test x"${py_ver}" == x"3.8" || test x"{py_ver}" == x"3.9"; then
+      if test x"${py_ver}" = x"3.8" || test x"{py_ver}" = x"3.9"; then
         PYTHON_LIBS="`\"$pycfg\" --ldflags --embed`"
       else
         PYTHON_LIBS="`\"$pycfg\" --ldflags`"