s3:mdssvc: fix flex compilation error

s3:mdssvc: fix flex compilation error

[4440/4495] Compiling bin/default/source3/rpc_server/mdssvc/sparql_lexer.lex.c
../../source3/rpc_server/mdssvc/sparql_lexer.l:26: error: "yyalloc" redefined [-Werror]
26 | #define yyalloc SMB_MALLOC

Looks like the dirty redefine trick doesn't work anymore with newer flex
versions. According to the flex manual the right thing to do is to provide own
functions for yyalloc and yyrealloc when passing the options "noyyalloc
noyyrealloc".

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Autobuild-User(master): Ralph Böhme <slow@samba.org>
Autobuild-Date(master): Tue May 28 11:49:06 UTC 2019 on sn-devel-184