autoconf: define NO_SYS_SELECT_H on systems without <sys/select.h>.

Pre-POSIX.1-2001 systems don't have <sys/select.h>, but select(2)
is declared in <sys/time.h>, which git-compat-util.h includes.
Signed-off-by: NJakub Narebski <jnareb@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

config.mak.in

@@ -30,6 +30,7 @@ NO_CURL=@NO_CURL@
 NO_EXPAT=@NO_EXPAT@
 NEEDS_LIBICONV=@NEEDS_LIBICONV@
 NEEDS_SOCKET=@NEEDS_SOCKET@
+NO_SYS_SELECT_H=@NO_SYS_SELECT_H@
 NO_D_INO_IN_DIRENT=@NO_D_INO_IN_DIRENT@
 NO_D_TYPE_IN_DIRENT=@NO_D_TYPE_IN_DIRENT@
 NO_SOCKADDR_STORAGE=@NO_SOCKADDR_STORAGE@

configure.ac

@@ -235,6 +235,12 @@ test -n "$NEEDS_SOCKET" && LIBS="$LIBS -lsocket"
 ## Checks for header files.
 AC_MSG_NOTICE([CHECKS for header files])
 #
+# Define NO_SYS_SELECT_H if you don't have sys/select.h.
+AC_CHECK_HEADER([sys/select.h],
+[NO_SYS_SELECT_H=],
+[NO_SYS_SELECT_H=UnfortunatelyYes])
+AC_SUBST(NO_SYS_SELECT_H)
+#
 # Define OLD_ICONV if your library has an old iconv(), where the second
 # (input buffer pointer) parameter is declared with type (const char **).
 AC_DEFUN([OLDICONVTEST_SRC], [[