build: assume errno.h is always available

- Remove errno.h detection from all build configurations.

errno.h is a standard header according to C89.

Closes https://github.com/curl/curl/pull/9986

CMakeLists.txt

@@ -975,7 +975,6 @@ check_include_file_concat("sys/utime.h"      HAVE_SYS_UTIME_H)
 check_include_file_concat("sys/xattr.h"      HAVE_SYS_XATTR_H)
 check_include_file_concat("arpa/inet.h"      HAVE_ARPA_INET_H)
 check_include_file_concat("arpa/tftp.h"      HAVE_ARPA_TFTP_H)
-check_include_file_concat("errno.h"          HAVE_ERRNO_H)
 check_include_file_concat("fcntl.h"          HAVE_FCNTL_H)
 check_include_file_concat("idn2.h"           HAVE_IDN2_H)
 check_include_file_concat("ifaddrs.h"        HAVE_IFADDRS_H)

configure.ac

@@ -3334,7 +3334,6 @@ AC_CHECK_HEADERS(
         sys/resource.h \
         libgen.h \
         locale.h \
-        errno.h \
         stdbool.h \
         arpa/tftp.h \
         sys/filio.h \

lib/config-amigaos.h

@@ -32,7 +32,6 @@
 
 #define HAVE_ARPA_INET_H 1
 #define HAVE_CLOSESOCKET_CAMEL 1
-#define HAVE_ERRNO_H 1
 #define HAVE_INTTYPES_H 1
 #define HAVE_IOCTLSOCKET_CAMEL 1
 #define HAVE_IOCTLSOCKET_CAMEL_FIONBIO 1

lib/config-dos.h

@@ -44,7 +44,6 @@
 #define USE_MANUAL 1
 
 #define HAVE_ARPA_INET_H       1
-#define HAVE_ERRNO_H           1
 #define HAVE_FCNTL_H           1
 #define HAVE_FREEADDRINFO      1
 #define HAVE_GETADDRINFO       1

lib/config-mac.h

@@ -37,7 +37,6 @@
 /* Define if you want the built-in manual */
 #define USE_MANUAL              1
 
-#define HAVE_ERRNO_H            1
 #define HAVE_NETINET_IN_H       1
 #define HAVE_SYS_SOCKET_H       1
 #define HAVE_NETDB_H            1

lib/config-os400.h

@@ -80,9 +80,6 @@
 /* Define if you have the `closesocket' function. */
 #undef HAVE_CLOSESOCKET
 
-/* Define if you have the <errno.h> header file. */
-#define HAVE_ERRNO_H
-
 /* Define if you have the <fcntl.h> header file. */
 #define HAVE_FCNTL_H
 

lib/config-plan9.h

@@ -78,7 +78,6 @@
 #define HAVE_ARPA_INET_H 1
 #define HAVE_BASENAME 1
 #define HAVE_BOOL_T 1
-#define HAVE_ERRNO_H 1
 #define HAVE_FCNTL 1
 #define HAVE_FCNTL_H 1
 #define HAVE_FREEADDRINFO 1

lib/config-riscos.h

@@ -81,9 +81,6 @@
 /* Define if you have the `closesocket' function. */
 #undef HAVE_CLOSESOCKET
 
-/* Define if you have the <errno.h> header file. */
-#define HAVE_ERRNO_H
-
 /* Define if you have the <fcntl.h> header file. */
 #define HAVE_FCNTL_H
 

lib/config-win32.h

@@ -35,9 +35,6 @@
 /* Define if you have the <arpa/inet.h> header file. */
 /* #define HAVE_ARPA_INET_H 1 */
 
-/* Define if you have the <errno.h> header file. */
-#define HAVE_ERRNO_H 1
-
 /* Define if you have the <fcntl.h> header file. */
 #define HAVE_FCNTL_H 1
 
@@ -339,7 +336,6 @@
 #  undef USE_WINSOCK
 #  undef HAVE_WINSOCK2_H
 #  undef HAVE_WS2TCPIP_H
-#  undef HAVE_ERRNO_H
 #  undef HAVE_GETHOSTNAME
 #  undef LWIP_POSIX_SOCKETS_IO_NAMES
 #  undef RECV_TYPE_ARG1

lib/config-win32ce.h

@@ -35,9 +35,6 @@
 /* Define if you have the <arpa/inet.h> header file.  */
 /* #define HAVE_ARPA_INET_H 1 */
 
-/* Define if you have the <errno.h> header file.  */
-/* #define HAVE_ERRNO_H 1 */
-
 /* Define if you have the <fcntl.h> header file.  */
 #define HAVE_FCNTL_H 1
 

lib/curl_config.h.cmake

@@ -171,9 +171,6 @@
 /* Define to 1 if you have the `closesocket' function. */
 #cmakedefine HAVE_CLOSESOCKET 1
 
-/* Define to 1 if you have the <errno.h> header file. */
-#cmakedefine HAVE_ERRNO_H 1
-
 /* Define to 1 if you have the fcntl function. */
 #cmakedefine HAVE_FCNTL 1
 

lib/curl_setup_once.h

@@ -34,10 +34,7 @@
 #include <string.h>
 #include <stdarg.h>
 #include <time.h>
-
-#ifdef HAVE_ERRNO_H
 #include <errno.h>
-#endif
 
 #ifdef HAVE_SYS_TYPES_H
 #include <sys/types.h>