Win32: patch Windows environment on startup

Fix Windows specific environment settings on startup rather than checking
for special values on every getenv call.

As a side effect, this makes the patched environment (i.e. with properly
initialized TMPDIR and TERM) available to child processes.

Signed-off-by: Karsten Blees <blees@dcon.de>
Signed-off-by: Stepan Kasal <kasal@ucw.cz>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

compat/mingw.c

@@ -1251,7 +1251,7 @@ static int do_putenv(char **env, const char *name, int size, int free_old)
 	return size;
 }
 
-static char *do_getenv(const char *name)
+char *mingw_getenv(const char *name)
 {
 	char *value;
 	int pos = bsearchenv(environ, name, environ_size - 1);
@@ -1261,18 +1261,6 @@ static char *do_getenv(const char *name)
 	return value ? &value[1] : NULL;
 }
 
-char *mingw_getenv(const char *name)
-{
-	char *result = do_getenv(name);
-	if (!result && !strcmp(name, "TMPDIR")) {
-		/* on Windows it is TMP and TEMP */
-		result = do_getenv("TMP");
-		if (!result)
-			result = do_getenv("TEMP");
-	}
-	return result;
-}
-
 int mingw_putenv(const char *namevalue)
 {
 	ALLOC_GROW(environ, (environ_size + 1) * sizeof(char*), environ_alloc);
@@ -2114,6 +2102,17 @@ void mingw_startup()
 	/* sort environment for O(log n) getenv / putenv */
 	qsort(environ, i, sizeof(char*), compareenv);
 
+	/* fix Windows specific environment settings */
+
+	/* on Windows it is TMP and TEMP */
+	if (!mingw_getenv("TMPDIR")) {
+		const char *tmp = mingw_getenv("TMP");
+		if (!tmp)
+			tmp = mingw_getenv("TEMP");
+		if (tmp)
+			setenv("TMPDIR", tmp, 1);
+	}
+
 	/* initialize critical section for waitpid pinfo_t list */
 	InitializeCriticalSection(&pinfo_cs);