configure: include <time.h> unconditionally

In 2682e5f5, several instances of AC_HEADER_TIME were removed since
it is a deprecated autoconf macro. However, this was the macro that
defined TIME_WITH_SYS_TIME, which was used to indicate that <time.h>
can be included alongside <sys/time.h>. TIME_WITH_SYS_TIME is still
used in the configure test body and since it is no longer defined,
<time.h> is *not* included on systems that have <sys/time.h>.

In particular, at least on musl libc and glibc, <sys/time.h> does
not implicitly include <time.h> and does not declare clock_gettime,
gmtime_r, or localtime_r. This causes configure to fail to detect
those functions.

The AC_HEADER_TIME macro deprecation text says

> All current systems provide time.h; it need not be checked for.
> Not all systems provide sys/time.h, but those that do, all allow
> you to include it and time.h simultaneously.

So, to fix this issue, simply include <time.h> unconditionally when
testing for time-related functions and in libcurl, and don't bother
checking for it.

Closes #6859

acinclude.m4

@@ -1410,7 +1410,7 @@ dnl Check for timeval struct
 AC_DEFUN([CURL_CHECK_STRUCT_TIMEVAL], [
   AC_REQUIRE([CURL_CHECK_HEADER_WINSOCK])dnl
   AC_REQUIRE([CURL_CHECK_HEADER_WINSOCK2])dnl
-  AC_CHECK_HEADERS(sys/types.h sys/time.h time.h sys/socket.h)
+  AC_CHECK_HEADERS(sys/types.h sys/time.h sys/socket.h)
   AC_CACHE_CHECK([for struct timeval], [curl_cv_struct_timeval], [
     AC_COMPILE_IFELSE([
       AC_LANG_PROGRAM([[
@@ -1433,14 +1433,8 @@ AC_DEFUN([CURL_CHECK_STRUCT_TIMEVAL], [
 #endif
 #ifdef HAVE_SYS_TIME_H
 #include <sys/time.h>
-#ifdef TIME_WITH_SYS_TIME
+#endif
 #include <time.h>
-#endif
-#else
-#ifdef HAVE_TIME_H
-#include <time.h>
-#endif
-#endif
 #ifdef HAVE_SYS_SOCKET_H
 #include <sys/socket.h>
 #endif
@@ -1605,7 +1599,7 @@ dnl -------------------------------------------------
 dnl Check if monotonic clock_gettime is available.
 
 AC_DEFUN([CURL_CHECK_FUNC_CLOCK_GETTIME_MONOTONIC], [
-  AC_CHECK_HEADERS(sys/types.h sys/time.h time.h)
+  AC_CHECK_HEADERS(sys/types.h sys/time.h)
   AC_MSG_CHECKING([for monotonic clock_gettime])
   #
   if test "x$dontwant_rt" = "xno" ; then
@@ -1616,14 +1610,8 @@ AC_DEFUN([CURL_CHECK_FUNC_CLOCK_GETTIME_MONOTONIC], [
 #endif
 #ifdef HAVE_SYS_TIME_H
 #include <sys/time.h>
-#ifdef TIME_WITH_SYS_TIME
+#endif
 #include <time.h>
-#endif
-#else
-#ifdef HAVE_TIME_H
-#include <time.h>
-#endif
-#endif
       ]],[[
         struct timespec ts;
         (void)clock_gettime(CLOCK_MONOTONIC, &ts);
@@ -1670,14 +1658,8 @@ AC_DEFUN([CURL_CHECK_LIBS_CLOCK_GETTIME_MONOTONIC], [
 #endif
 #ifdef HAVE_SYS_TIME_H
 #include <sys/time.h>
-#ifdef TIME_WITH_SYS_TIME
+#endif
 #include <time.h>
-#endif
-#else
-#ifdef HAVE_TIME_H
-#include <time.h>
-#endif
-#endif
           ]],[[
             struct timespec ts;
             (void)clock_gettime(CLOCK_MONOTONIC, &ts);
@@ -1725,14 +1707,8 @@ AC_DEFUN([CURL_CHECK_LIBS_CLOCK_GETTIME_MONOTONIC], [
 #endif
 #ifdef HAVE_SYS_TIME_H
 #include <sys/time.h>
-#ifdef TIME_WITH_SYS_TIME
+#endif
 #include <time.h>
-#endif
-#else
-#ifdef HAVE_TIME_H
-#include <time.h>
-#endif
-#endif
         ]],[[
           struct timespec ts;
           if (0 == clock_gettime(CLOCK_MONOTONIC, &ts))
@@ -1902,14 +1878,8 @@ AC_DEFUN([CURL_CHECK_FUNC_SELECT], [
 #endif
 #ifdef HAVE_SYS_TIME_H
 #include <sys/time.h>
-#ifdef TIME_WITH_SYS_TIME
+#endif
 #include <time.h>
-#endif
-#else
-#ifdef HAVE_TIME_H
-#include <time.h>
-#endif
-#endif
 #ifndef HAVE_WINDOWS_H
 #ifdef HAVE_SYS_SELECT_H
 #include <sys/select.h>
@@ -1967,14 +1937,8 @@ struct Library *SocketBase = NULL;
 #endif
 #ifdef HAVE_SYS_TIME_H
 #include <sys/time.h>
-#ifdef TIME_WITH_SYS_TIME
+#endif
 #include <time.h>
-#endif
-#else
-#ifdef HAVE_TIME_H
-#include <time.h>
-#endif
-#endif
 #ifndef HAVE_WINDOWS_H
 #ifdef HAVE_SYS_SELECT_H
 #include <sys/select.h>

configure.ac

@@ -4277,7 +4277,6 @@ AC_CHECK_HEADERS(
         sgtty.h \
         fcntl.h \
         alloca.h \
-        time.h \
         io.h \
         pwd.h \
         utime.h \

lib/curl_setup_once.h

@@ -32,6 +32,7 @@
 #include <string.h>
 #include <stdarg.h>
 #include <ctype.h>
+#include <time.h>
 
 #ifdef HAVE_ERRNO_H
 #include <errno.h>
@@ -55,13 +56,6 @@
 
 #ifdef HAVE_SYS_TIME_H
 #include <sys/time.h>
-#ifdef TIME_WITH_SYS_TIME
-#include <time.h>
-#endif
-#else
-#ifdef HAVE_TIME_H
-#include <time.h>
-#endif
 #endif
 
 #ifdef WIN32

m4/curl-functions.m4

@@ -453,17 +453,11 @@ curl_includes_time="\
 #endif
 #ifdef HAVE_SYS_TIME_H
 #  include <sys/time.h>
-#  ifdef TIME_WITH_SYS_TIME
-#    include <time.h>
-#  endif
-#else
-#  ifdef HAVE_TIME_H
-#    include <time.h>
-#  endif
 #endif
+#include <time.h>
 /* includes end */"
   AC_CHECK_HEADERS(
-    sys/types.h sys/time.h time.h,
+    sys/types.h sys/time.h,
     [], [], [$curl_includes_time])
 ])