Port plugin building to AMBuild.

Former-commit-id: 9ac73de5b247da341b0b4cdf00ec3c7e0472be82

compiler/libpc300/sc.h

@@ -763,6 +763,7 @@ SC_VDECL int sc_needsemicolon;/* semicolon required to terminate expressions? */
 SC_VDECL int sc_dataalign;    /* data alignment value */
 SC_VDECL int sc_alignnext;    /* must frame of the next function be aligned? */
 SC_VDECL int pc_docexpr;      /* must expression be attached to documentation comment? */
+SC_VDECL int sc_showincludes; /* show include files? */
 SC_VDECL int curseg;          /* 1 if currently parsing CODE, 2 if parsing DATA */
 SC_VDECL cell sc_stksize;     /* stack size */
 SC_VDECL cell sc_amxlimit;    /* abstract machine size limit */