Reduce size of RESERVED_BRK_SPACE for A32

For unknown reasons when RESERVED_BRK_SPACE is set to 128 * PAGE_SIZE
MABMO segfaults on scanning the first instructions. The problem
first transpires after mmap and remmap involving RESERVED_BRK_SPACE
is executed. This fix reduces the reserved space back to PAGE_SIZE
for A32 - the value used before RISC-V merge. One of the possible
explnations is smaller virtual memory on A32 compared to A64 and RISC-V.

dbm.h

@@ -69,7 +69,11 @@
 #define MAX_CC_LINKS 100000
 
 // The size of the initial data segment allocation for brk emulation
-#define RESERVED_BRK_SPACE (128*(PAGE_SIZE))
+#ifdef __arm__
+  #define RESERVED_BRK_SPACE (PAGE_SIZE)
+#else
+  #define RESERVED_BRK_SPACE (128*(PAGE_SIZE))
+#endif
 
 #if defined __arm__ || __aarch64__ 
 #define THUMB 0x1