test557: set a known good numeric locale

Windows does not allow setting the locale with environment variables (as
the test attempted to do), so the test failed when run with a user
locale that has a comma as radixchar. Changed the test to call
setlocale() explicitly to ensure that a known working locale is set even
on Windows.

tests/data/test557

@@ -15,10 +15,6 @@ unittest
 <server>
 none
 </server>
-<setenv>
-LC_ALL=
-LC_NUMERIC=C
-</setenv>
 # tool is what to use instead of 'curl'
 <tool>
 lib557

tests/libtest/lib557.c

@@ -26,8 +26,12 @@
  */
 
 #include "test.h"
-#include "memdebug.h"
 
+#ifdef HAVE_LOCALE_H
+#  include <locale.h> /* for setlocale() */
+#endif
+
+#include "memdebug.h"
 
 #if (CURL_SIZEOF_CURL_OFF_T > CURL_SIZEOF_LONG)
 #  define MPRNT_SUFFIX_CURL_OFF_T  LL
@@ -1656,6 +1660,14 @@ int test(char *URL)
   int errors = 0;
   (void)URL; /* not used */
 
+#ifdef HAVE_SETLOCALE
+  /*
+   * The test makes assumptions about the numeric locale (specifically,
+   * RADIXCHAR) so set it to a known working (and portable) one.
+   */
+  setlocale(LC_NUMERIC, "C");
+#endif
+
   errors += test_weird_arguments();
 
   errors += test_unsigned_short_formatting();