asteris-chan-sccp: fix compile for sccp

Provide forward declarations which are absent during compile
to resolve compile error. Compile tested only in the hope
it's useful.

Signed-off-by: Paul Donald <newtwen+github@gmail.com>

Author: systemcrash

net/asterisk-chan-sccp/patches/03-compile-fix.patch

@@ -0,0 +1,18 @@
+diff --git a/src/pbx_impl/ast116/ast116.c b/src/pbx_impl/ast116/ast116.c
+index c162e755..6fa5b610 100644
+--- a/src/pbx_impl/ast116/ast116.c
++++ b/src/pbx_impl/ast116/ast116.c
+@@ -61,6 +61,13 @@ __BEGIN_C_EXTERN__
+ #include <asterisk/format_cap.h>		// for AST_FORMAT_CAP_NAMES_LEN
+ #include <asterisk/say.h>                                        // PARKING
+ 
++/* Provide forward declarations in case they are missing.  Duplicate
++ * declarations are harmless. */
++const char *ast_channel_macroexten(const struct ast_channel *chan);
++void ast_channel_macroexten_set(struct ast_channel *chan, const char *value);
++const char *ast_channel_macrocontext(const struct ast_channel *chan);
++void ast_channel_macrocontext_set(struct ast_channel *chan, const char *value);
++
+ #define new avoid_cxx_new_keyword
+ #include <asterisk/rtp_engine.h>
+ #undef new