[builds] Add comment for the `BIN' variable.

Separate the definition of `BIN' in `*def.mk' files and add a comment
stating that it is being used for `make refdoc' and `make refdoc-venv'.

builds/ansi/ansi-def.mk

@@ -16,10 +16,12 @@
 DELETE    := rm -f
 CAT       := cat
 SEP       := /
-BIN       := bin
 BUILD_DIR := $(TOP_DIR)/builds/ansi
 PLATFORM  := ansi
 
+# This is used for `make refdoc' and `make refdoc-venv'
+#
+BIN    := bin
 
 # The directory where all library files are placed.
 #

builds/beos/beos-def.mk

@@ -18,10 +18,12 @@
 DELETE    := rm -f
 CAT       := cat
 SEP       := /
-BIN       := bin
 BUILD_DIR := $(TOP_DIR)/builds/beos
 PLATFORM  := beos
 
+# This is used for `make refdoc' and `make refdoc-venv'
+#
+BIN    := bin
 
 # The directory where all library files are placed.
 #

builds/dos/dos-def.mk

@@ -16,10 +16,12 @@
 DELETE    := del
 CAT       := type
 SEP       := $(strip \ )
-BIN       := Scripts
 BUILD_DIR := $(TOP_DIR)/builds/dos
 PLATFORM  := dos
 
+# This is used for `make refdoc' and `make refdoc-venv'
+#
+BIN    := Scripts
 
 # The executable file extension (for tools), *with* leading dot.
 #

builds/os2/os2-def.mk

@@ -16,10 +16,13 @@
 DELETE    := del
 CAT       := type
 SEP       := $(strip \ )
-BIN       := Scripts
 BUILD_DIR := $(TOP_DIR)/builds/os2
 PLATFORM  := os2
 
+# This is used for `make refdoc' and `make refdoc-venv'
+#
+BIN    := Scripts
+
 # The executable file extension (for tools), *with* leading dot.
 #
 E := .exe

builds/unix/unix-def.in

@@ -21,7 +21,7 @@ DELDIR := rm -rf
 CAT    := cat
 SEP    := /
 
-# this is used for `make refdoc' and `make refdoc-venv'
+# This is used for `make refdoc' and `make refdoc-venv'
 #
 PYTHON := @PYTHON@
 PIP    := @PIP@

builds/unix/unixddef.mk

@@ -22,6 +22,9 @@ PLATFORM := unix
 DELETE := rm -f
 CAT    := cat
 SEP    := /
+
+# This is used for `make refdoc' and `make refdoc-venv'
+#
 BIN    := bin
 
 # we use a special devel ftoption.h

builds/windows/win32-def.mk

@@ -16,10 +16,13 @@
 DELETE    := del
 CAT       := type
 SEP       := $(strip \ )
-BIN       := Scripts
 BUILD_DIR := $(TOP_DIR)/builds/windows
 PLATFORM  := windows
 
+# This is used for `make refdoc' and `make refdoc-venv'
+#
+BIN    := Scripts
+
 # The executable file extension (for tools). NOTE: WE INCLUDE THE DOT HERE !!
 #
 E := .exe