feature test macros: make _GNU_SOURCE enable everything

previously, a few BSD features were enabled only by _BSD_SOURCE, not
by _GNU_SOURCE. since _BSD_SOURCE is default in the absence of other
feature test macros, this made adding _GNU_SOURCE to a project not a
purely additive feature test macro; it actually caused some features
to be suppressed.

most of the changes made by this patch actually bring musl in closer
alignment with the glibc behavior for _GNU_SOURCE. the only exceptions
are the added visibility of functions like strlcpy which were BSD-only
due to being disliked/rejected by glibc maintainers. here, I feel the
consistency of having _GNU_SOURCE mean "everything", and especially
the property of it being purely additive, are more valuable than
hiding functions which glibc does not have.

include/dirent.h

@@ -9,7 +9,7 @@ extern "C" {
 
 #define __NEED_ino_t
 #define __NEED_off_t
-#ifdef _BSD_SOURCE
+#if defined(_BSD_SOURCE) || defined(_GNU_SOURCE)
 #define __NEED_size_t
 #endif
 
@@ -53,16 +53,13 @@ int scandir(const char *, struct dirent ***, int (*)(const struct dirent *), int
 #define DT_WHT 14
 #define IFTODT(x) ((x)>>12 & 017)
 #define DTTOIF(x) ((x)<<12)
+int getdents(int, struct dirent *, size_t);
 #endif
 
 #ifdef _GNU_SOURCE
 int versionsort(const struct dirent **, const struct dirent **);
 #endif
 
-#ifdef _BSD_SOURCE
-int getdents(int, struct dirent *, size_t);
-#endif
-
 #if defined(_LARGEFILE64_SOURCE) || defined(_GNU_SOURCE)
 #define dirent64 dirent
 #define readdir64 readdir
@@ -72,10 +69,8 @@ int getdents(int, struct dirent *, size_t);
 #define versionsort64 versionsort
 #define off64_t off_t
 #define ino64_t ino_t
-#ifdef _BSD_SOURCE
 #define getdents64 getdents
 #endif
-#endif
 
 #ifdef __cplusplus
 }

include/signal.h

@@ -212,7 +212,7 @@ void (*sigset(int, void (*)(int)))(int);
 #define NSIG _NSIG
 #endif
 
-#ifdef _BSD_SOURCE
+#if defined(_BSD_SOURCE) || defined(_GNU_SOURCE)
 typedef void (*sig_t)(int);
 #endif
 

include/stdio.h

@@ -174,9 +174,6 @@ int ferror_unlocked(FILE *);
 int fileno_unlocked(FILE *);
 int getw(FILE *);
 int putw(int, FILE *);
-#endif
-
-#ifdef _BSD_SOURCE
 char *fgetln(FILE *, size_t *);
 #endif
 

include/string.h

@@ -81,9 +81,6 @@ void *memccpy (void *__restrict, const void *__restrict, int, size_t);
 
 #if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
 char *strsep(char **, const char *);
-#endif
-
-#ifdef _BSD_SOURCE
 size_t strlcat (char *, const char *, size_t);
 size_t strlcpy (char *, const char *, size_t);
 #endif

include/sys/stat.h

@@ -88,11 +88,8 @@ int mkfifoat(int, const char *, mode_t);
 int futimens(int, const struct timespec [2]);
 int utimensat(int, const char *, const struct timespec [2], int);
 
-#ifdef _BSD_SOURCE
-int lchmod(const char *, mode_t);
-#endif
-
 #if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
+int lchmod(const char *, mode_t);
 #define S_IREAD S_IRUSR
 #define S_IWRITE S_IWUSR
 #define S_IEXEC S_IXUSR