Fix DMDSRC and allow a PROJECT_SOURCE_DIR to be set by DMD

Author: wilzbach

dlang.org.ddoc

@@ -136,7 +136,7 @@ DDOCKEYVAL2=$(DIVC keyval $1, $(SPANC key key$1, $2:) $(DIVC val val$1, $(TAIL $
 DDSUBLINK=$(LINK2 $(ROOT_DIR)$1.html#$2, $3)
 _=
 
-DMDSRC=$(HTTPS github.com/D-Programming-Language/dmd/blob/master/src/$0, $0)
+DMDSRC=$(HTTPS github.com/dlang/dmd/blob/master/src/dmd/$0, $0)
 DOT_PREFIXED=.$1$(DOT_PREFIXED $+)
 DOT_PREFIXED_SKIP=$(DOT_PREFIXED $+)
 DRUNTIMESRC=$(HTTPS github.com/dlang/druntime/blob/master/src/$0, $0)
@@ -282,7 +282,7 @@ $(DIVID tools, $(DIV,
 		)
 	)
 	$(DIVC tip smallprint,
-		<a href="https://github.com/dlang/$(PROJECT)/edit/master/$(SRCFILENAME)">Improve this page</a>
+		<a href="https://github.com/dlang/$(PROJECT)/edit/master/$(PROJECT_SOURCE_DIR)$(SRCFILENAME)">Improve this page</a>
 		$(DIV,
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@@ -486,4 +486,6 @@ _=
 
 YELLOW=$(SPANC yellow, $0)
 YES=$(CHECKMARK)
+
+PROJECT_SOURCE_DIR=
 _=