fix missing limits when only _BSD_SOURCE is defined

the missing check did not affect the default profile, since it has
both _XOPEN_SOURCE and _BSD_SOURCE defined, but it did break programs
which explicitly define _BSD_SOURCE, causing it to be the only feature
test macro present.

include/limits.h

@@ -37,7 +37,7 @@
 #define MB_LEN_MAX 4
 
 #if defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE) \
- || defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE)
+ || defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
 
 #define PIPE_BUF 4096
 #define PAGESIZE PAGE_SIZE