Add strftime_l to the library. Only the C locale is supported.

* Makefile, NEWS: Document this.
* private.h (HAVE_STRFTIME_L): New macro.
* strftime.c (strftime_l) [HAVE_STRFTIME_L]: New function.

Makefile

@@ -115,6 +115,8 @@ LDLIBS=
 #  -DHAVE_SETTIMEOFDAY=2 if settimeofday uses 2nd arg (4.3BSD)
 #  -DHAVE_SETTIMEOFDAY=3 if settimeofday ignores 2nd arg (4.4BSD)
 #  -DHAVE_STDINT_H=1 if you have a pre-C99 compiler with "stdint.h"
+#  -DHAVE_STRFTIME_L=1 if <time.h> declares locale_t and strftime_l
+#	This defaults to 0 if _POSIX_VERSION < 200809, 1 otherwise.
 #  -DHAVE_SYMLINK=0 if your system lacks the symlink function
 #  -DHAVE_SYS_STAT_H=0 if your compiler lacks a "sys/stat.h"
 #  -DHAVE_SYS_WAIT_H=0 if your compiler lacks a "sys/wait.h"

NEWS

@@ -67,6 +67,11 @@ Unreleased, experimental changes
     more likely to guess right for ambiguous time stamps near
     transitions where tm_isdst does not change.
 
+    If HAVE_STRFTIME_L is defined to 1, the tz library now defines
+    strftime_l for compatibility with recent versions of POSIX.
+    Only the C locale is supported, though.  HAVE_STRFTIME_L defaults
+    to 1 on recent POSIX versions, and to 0 otherwise.
+
     zdump now builds with the tz library unless USE_LTZ is defined to 0,
     This lets zdump use tz features even if the system library lacks them.
     To build zdump with the system library, use 'make CFLAGS=-DUSE_LTZ=0

private.h

@@ -101,6 +101,14 @@
 #include "unistd.h"	/* for F_OK, R_OK, and other POSIX goodness */
 #endif /* HAVE_UNISTD_H */
 
+#ifndef HAVE_STRFTIME_L
+# if _POSIX_VERSION < 200809
+#  define HAVE_STRFTIME_L 0
+# else
+#  define HAVE_STRFTIME_L 1
+# endif
+#endif
+
 #ifndef F_OK
 #define F_OK	0
 #endif /* !defined F_OK */

strftime.c

@@ -106,6 +106,16 @@ extern char *	tzname[];
 #define IN_THIS	2
 #define IN_ALL	3
 
+#if HAVE_STRFTIME_L
+size_t
+strftime_l(char *s, size_t maxsize, char const *format, struct tm const *t,
+	   locale_t locale)
+{
+  /* Just call strftime, as only the C locale is supported.  */
+  return strftime(s, maxsize, format, t);
+}
+#endif
+
 size_t
 strftime(char * const s, const size_t maxsize, const char *const format,
 	 const struct tm *const t)