[PATCH] Fix build breakage on MinGW due to missing setenv

[Anton Kolesov <Anton.Kolesov@synopsys.com>]

Patch [1] broke a build on MinGW hosts, because MinGW doesn't provide POSIX
functions setenv () and unsetenv (), instead there is a putenv () wrapper
around WinAPI function, although with a different signature.

[1] https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=9a6c7d9c0

gdb/ChangeLog
yyyy-mm-dd  Anton Kolesov  <Anton.Kolesov@synopsys.com>

	* unittests/environ-selftests.c (run_tests): Use putenv on MinGW.
---
 gdb/unittests/environ-selftests.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/gdb/unittests/environ-selftests.c b/gdb/unittests/environ-selftests.c
index 28b16f8..8872bfa 100644
--- a/gdb/unittests/environ-selftests.c
+++ b/gdb/unittests/environ-selftests.c
@@ -30,7 +30,11 @@ run_tests ()
 {
   /* Set a test environment variable.  This will be unset at the end
      of this function.  */
+#ifndef USE_WIN32API
   if (setenv ("GDB_SELFTEST_ENVIRON", "1", 1) != 0)
+#else
+  if (putenv ("GDB_SELFTEST_ENVIRON=1") != 0)
+#endif
     error (_("Could not set environment variable for testing."));
 
   gdb_environ env;
@@ -90,7 +94,13 @@ run_tests ()
   SELF_CHECK (num_found == 1);
 
   /* Get rid of our test variable.  */
+#ifndef USE_WIN32API
   unsetenv ("GDB_SELFTEST_ENVIRON");
+#else
+  /* putenv ("var=") has the same meaning as unsetenv ("var"), unlike the
+     setenv ("var="), which would assign an empty value.  */
+  putenv ("GDB_SELFTEST_ENVIRON=");
+#endif
 
   /* Test the case when we set a variable A, then set a variable B,
      then unset A, and make sure that we cannot find A in the environ
-- 
2.8.3