Drop deprecated macro from configure.ac

Author: yoe

configure.ac

@@ -107,7 +107,7 @@ AC_ARG_ENABLE(
   [ENABLE_GZNBD=no]
 )
 
-AC_PROG_CC_C99
+AC_PROG_CC
 AC_PROG_CPP
 AC_PROG_INSTALL
 AM_PROG_LEX(noyywrap)
@@ -267,7 +267,6 @@ AC_CHECK_FUNC([sync_file_range],
 	[AC_DEFINE([HAVE_SYNC_FILE_RANGE], [sync_file_range(2) is not supported], [sync_file_range(2) is supported])],
         [])
 AC_FUNC_FORK
-AC_FUNC_SETVBUF_REVERSED
 AC_MSG_CHECKING(whether client should be built)
 AS_CASE([$host_os],
   [linux*], [NBD_CLIENT_NAME="nbd-client"; AC_MSG_RESULT(yes)],