Fix build for some non-x86 archs

Ref:
https://buildd.debian.org/status/fetch.php?pkg=finit&arch=mips64el&ver=3.2%7Erc3-2&stamp=1609910244&raw=0
https://buildd.debian.org/status/fetch.php?pkg=finit&arch=sparc64&ver=3.2%7Erc3-2&stamp=1609869348&raw=0

src/sig.c

@@ -138,7 +138,9 @@ static struct sigmap {
 	/* Nonstandard signals found in all modern POSIX systems
 	   (including both BSD and Linux).  */
 	{ SIGWINCH,  "SIGWINCH"  },
+#ifdef SIGSTKFLT
 	{ SIGSTKFLT, "SIGSTKFLT" },
+#endif
 	{ SIGPWR,    "SIGPWR"    },
 
 	/* Archaic names for compatibility.  */

src/stty.c

@@ -61,10 +61,12 @@ speed_t stty_parse_speed(char *baud)
 		{ 1152000, B1152000 },
 		{ 1500000, B1500000 },
 		{ 2000000, B2000000 },
+#ifdef B4000000
 		{ 2500000, B2500000 },
 		{ 3000000, B3000000 },
 		{ 3500000, B3500000 },
 		{ 4000000, B4000000 },
+#endif
 	};
 
 	if (!baud || !baud[0])