pager: set LESS=FRSX also on Windows

Previously, this environment variable was set in the pager_preexec
callback, which is conditionally-compiled only on Unix, because it is not,
and cannot be, called on Windows.

With this patch the env member of struct child_process is used to set
the environment variable, which also works on Windows.

Noticed by Alexey Borzenkov.
Signed-off-by: NJohannes Sixt <j6t@kdbg.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

pager.c

@@ -21,8 +21,6 @@ static void pager_preexec(void)
 	FD_ZERO(&in);
 	FD_SET(0, &in);
 	select(1, &in, NULL, &in, NULL);
-
-	setenv("LESS", "FRSX", 0);
 }
 #endif
 
@@ -70,6 +68,10 @@ void setup_pager(void)
 	pager_argv[2] = pager;
 	pager_process.argv = pager_argv;
 	pager_process.in = -1;
+	if (!getenv("LESS")) {
+		static const char *env[] = { "LESS=FRSX", NULL };
+		pager_process.env = env;
+	}
 #ifndef __MINGW32__
 	pager_process.preexec_cb = pager_preexec;
 #endif