configure: test whether -lresolv is needed

Check if -lresolv is needed for hstrerror; set NEEDS_RESOLV
accordingly, and substitute in config.mak.in.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

config.mak.in

@@ -32,6 +32,7 @@ NO_CURL=@NO_CURL@
 NO_EXPAT=@NO_EXPAT@
 NEEDS_LIBICONV=@NEEDS_LIBICONV@
 NEEDS_SOCKET=@NEEDS_SOCKET@
+NEEDS_RESOLV=@NEEDS_RESOLV@
 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@

configure.ac

@@ -467,6 +467,15 @@ AC_CHECK_LIB([c], [socket],
 AC_SUBST(NEEDS_SOCKET)
 test -n "$NEEDS_SOCKET" && LIBS="$LIBS -lsocket"
 
+#
+# Define NEEDS_RESOLV if linking with -lnsl and/or -lsocket is not enough.
+# Notably on Solaris hstrerror resides in libresolv and on Solaris 7
+# inet_ntop and inet_pton additionally reside there.
+AC_CHECK_LIB([resolv], [hstrerror],
+[NEEDS_RESOLV=],
+[NEEDS_RESOLV=YesPlease])
+AC_SUBST(NEEDS_RESOLV)
+test -n "$NEEDS_RESOLV" && LIBS="$LIBS -lresolv"
 
 ## Checks for header files.
 AC_MSG_NOTICE([CHECKS for header files])