BeOS doesn't have mmap. Also, BeOS is case sensitive like Unix.

modules/libreg/src/Makefile.in

@@ -36,8 +36,8 @@ MKSHLIB :=
 
 include $(topsrcdir)/config/config.mk
 
-# Memory mapped files are not supported under QNX and Neutrino
+# Memory mapped files are not supported under QNX, Neutrino and BeOS
-ifneq ($(OS_ARCH),QNX)
+ifeq (,$(filter BeOS QNX,$(OS_ARCH)))
 DEFINES += -DUSE_MMAP_REGISTRY_IO
 CSRCS += mmapio.c
 endif

modules/libreg/src/reg.c

@@ -310,7 +310,7 @@ static REGFILE* vr_findRegFile(char *filename)
 
     pReg = RegList;
     while( pReg != NULL ) {
-#ifdef XP_UNIX
+#if defined XP_UNIX || defined XP_BEOS
         if ( 0 == XP_STRCMP( filename, pReg->filename ) ) {
 #else
         if ( 0 == XP_STRCASECMP( filename, pReg->filename ) ) {