pidl: optionally annotate output for debug purposes

pidl: optionally annotate output for debug purposes

It can sometimes be hard to tell which bit of pidl generated which bit
of C. This commit wants to help.

If the PIDL_DEVELOPER environment variable is set (via waf
--pidl-developer or some other means), pidl will annotate *most* C
indicating which lines were generated by which bits of pidl. It looks
something like this:

_PUBLIC_ enum ndr_err_code ndr_push_auth_session_info(struct ndr_push *ndr, int ndr_flags, const struct auth_session_info *r)
{  //:PIDL: Parse::Pidl::Samba4::NDR::Parser::ParseTypePushFunction  lib/Parse/Pidl/Samba4/NDR/Parser.pm:3079
	NDR_PUSH_CHECK_FLAGS(ndr, ndr_flags);  //:PIDL: Parse::Pidl::Samba4::NDR::Parser::ParseStructPush  lib/Parse/Pidl/Samba4/NDR/Parser.pm:604
	if (ndr_flags & NDR_SCALARS) {
		NDR_CHECK(ndr_push_align(ndr, 5));  //:PIDL: Parse::Pidl::Samba4::NDR::Parser::ParseStructPushPrimitives  lib/Parse/Pidl/Samba4/NDR/Parser.pm:1448
		NDR_CHECK(ndr_push_unique_ptr(ndr, r->security_token));  //:PIDL: Parse::Pidl::Samba4::NDR::Parser::ParsePtrPush  lib/Parse/Pidl/Samba4/NDR/Parser.pm:604
		NDR_CHECK(ndr_push_unique_ptr(ndr, r->unix_token));
		NDR_CHECK(ndr_push_unique_ptr(ndr, r->info));
		NDR_CHECK(ndr_push_unique_ptr(ndr, r->unix_info));
		NDR_CHECK(ndr_push_uint3264(ndr, NDR_SCALARS, 0));
		/* [ignore] 'torture' */  //:PIDL: Parse::Pidl::Samba4::NDR::Parser::ParseElementPushLevel  lib/Parse/Pidl/Samba4/NDR/Parser.pm:729
		NDR_CHECK(ndr_push_DATA_BLOB(ndr, NDR_SCALARS, r->session_key));  //:PIDL: Parse::Pidl::Samba4::NDR::Parser::ParseDataPush  lib/Parse/Pidl/Samba4/NDR/Parser.pm:604
		NDR_CHECK(ndr_push_uint3264(ndr, NDR_SCALARS, 0));  //:PIDL: Parse::Pidl::Samba4::NDR::Parser::ParsePtrPush  lib/Parse/Pidl/Samba4/NDR/Parser.pm:604
		/* [ignore] 'credentials' */  //:PIDL: Parse::Pidl::Samba4::NDR::Parser::ParseElementPushLevel  lib/Parse/Pidl/Samba4/NDR/Parser.pm:729

The comments starting with '//:PIDL:' have the function name, the filename,
and line number. The comment follows the ordinary output, and uses the '//'
style so as not to interfere with multiline /* */ comments if they happen
to exist.

A '//:PIDL:' comment is added whenever the pidl function or indentation
level changes, and very occasionally at other places if pidl runs for a
while without either of these things happening.

This does not affect pidl parsers that do not inherit from Parse::Pidl::Base,
and is careful to have no performance impact on non-debug generation.

This may help with semi-automated flow analysis.

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>