Adjust makefiles to work with out-of-tree builds

This is based on work done by Larry Doolittle

frontends/verilog/Makefile.inc

@@ -5,13 +5,15 @@ GENFILES += frontends/verilog/verilog_parser.output
 GENFILES += frontends/verilog/verilog_lexer.cc
 
 frontends/verilog/verilog_parser.tab.cc: frontends/verilog/verilog_parser.y
-	$(P) $(BISON) -d -r all -b frontends/verilog/verilog_parser frontends/verilog/verilog_parser.y
+	$(Q) mkdir -p $(dir $@)
+	$(P) $(BISON) -d -r all -b frontends/verilog/verilog_parser $<
 	$(Q) mv frontends/verilog/verilog_parser.tab.c frontends/verilog/verilog_parser.tab.cc
 
 frontends/verilog/verilog_parser.tab.h: frontends/verilog/verilog_parser.tab.cc
 
 frontends/verilog/verilog_lexer.cc: frontends/verilog/verilog_lexer.l
-	$(P) flex -o frontends/verilog/verilog_lexer.cc frontends/verilog/verilog_lexer.l
+	$(Q) mkdir -p $(dir $@)
+	$(P) flex -o frontends/verilog/verilog_lexer.cc $<
 
 OBJS += frontends/verilog/verilog_parser.tab.o
 OBJS += frontends/verilog/verilog_lexer.o

frontends/verilog/verilog_lexer.l

@@ -40,7 +40,7 @@
 #endif
 
 #include "kernel/log.h"
-#include "verilog_frontend.h"
+#include "frontends/verilog/verilog_frontend.h"
 #include "frontends/ast/ast.h"
 #include "verilog_parser.tab.h"
 

frontends/verilog/verilog_parser.y

@@ -36,7 +36,7 @@
 %{
 #include <list>
 #include <string.h>
-#include "verilog_frontend.h"
+#include "frontends/verilog/verilog_frontend.h"
 #include "kernel/log.h"
 
 USING_YOSYS_NAMESPACE