build: BCC - recover lost functionality from commit 3d813204

Borland's $(MAKEDIR) expands to the path where make.exe is located,
use this feature to define BCCDIR when user has not defined BCCDIR.

lib/Makefile.b32

@@ -10,9 +10,10 @@
 #  Written by Jaepil Kim, pit@paradise.net.nz
 ############################################################
 
-# Check if BCCDIR is set.
-!if !$d(BCCDIR)
-!error BCCDIR not defined
+# Borland's $(MAKEDIR) expands to the path where make.exe is located,
+# use this feature to define BCCDIR when user has not defined BCCDIR.
+!if "$(BCCDIR)" == ""
+BCCDIR = $(MAKEDIR)\..
 !endif
 
 # Edit the path below to point to the base of your Zlib sources.

src/Makefile.b32

@@ -10,9 +10,10 @@
 #  Written by Jaepil Kim, pit@paradise.net.nz
 ############################################################
 
-# Check if BCCDIR is set.
-!if !$d(BCCDIR)
-!error BCCDIR not defined
+# Borland's $(MAKEDIR) expands to the path where make.exe is located,
+# use this feature to define BCCDIR when user has not defined BCCDIR.
+!if "$(BCCDIR)" == ""
+BCCDIR = $(MAKEDIR)\..
 !endif
 
 # Edit the path below to point to the base of your Zlib sources.