Makefile: remove 32bit thunk compilation by default

Compiling in 32bit mode is broken, and we don't have an intention on
restarting compatibility with 32bit apps.

Change-Id: I5524b5b63fe62e6026aa04d84c4510e290a86106

src/Makefile

@@ -39,7 +39,7 @@ OBJS = debug.o globals.o memory.o perfctr.o time.o version.o \
 .PHONY: all lnx lnx64a clean
 
 # Default target
-all: lnx lnx64a
+all: lnx64a
 
 # To relocate build output, set "O=target/dir/"
 # otherwise it defaults to a local directory