add missing confstr constants

the _CS_V6_ENV and _CS_V7_ENV constants are required to be available for use
with confstr. glibc defines these constants with values 1148 and 1149,
respectively.

the only missing (and required) confstr constants are
_CS_POSIX_V7_THREADS_CFLAGS and _CS_POSIX_V7_THREADS_LDFLAGS which remain
unavailable in glibc.

include/unistd.h

@@ -457,6 +457,8 @@ int eaccess(const char *, int);
 #define _CS_POSIX_V7_LPBIG_OFFBIG_LDFLAGS	1145
 #define _CS_POSIX_V7_LPBIG_OFFBIG_LIBS	1146
 #define _CS_POSIX_V7_LPBIG_OFFBIG_LINTFLAGS	1147
+#define _CS_V6_ENV	1148
+#define _CS_V7_ENV	1149
 
 #ifdef __cplusplus
 }

src/conf/confstr.c

@@ -7,7 +7,7 @@ size_t confstr(int name, char *buf, size_t len)
 	const char *s = "";
 	if (!name) {
 		s = "/bin:/usr/bin";
-	} else if ((name&~4U)!=1 && name-_CS_POSIX_V6_ILP32_OFF32_CFLAGS>31U) {
+	} else if ((name&~4U)!=1 && name-_CS_POSIX_V6_ILP32_OFF32_CFLAGS>33U) {
 		errno = EINVAL;
 		return 0;
 	}