force -O1 to reduce memory presssure when building disasm.cc

Index: disasm/disasm.mk.in
--- disasm/disasm.mk.in.orig
+++ disasm/disasm.mk.in
@@ -1,4 +1,4 @@
-disasm_CFLAGS = -fPIC
+disasm_CFLAGS = -fPIC -O1
 
 disasm_srcs = \
   disasm.cc \