fixup! build.sh: deduplicate cc -dM -E output and automate __BLST_NO_ASM__.

Author: dot-asm

build.sh

@@ -67,7 +67,7 @@ if [ "x$CROSS_COMPILE" = "x" ]; then
                           else     { print $1 } }'`
 fi
 
-predefs=`(${CC} ${CFLAGS} -dM -E -x c /dev/null) 2>/dev/null`
+predefs=`(${CC} ${CFLAGS} -dM -E -x c /dev/null || true) 2>/dev/null`
 
 if [ -z "${CROSS_COMPILE}${AR}" ] && echo ${predefs} | grep -q clang; then
     search_dirs=`${CC} -print-search-dirs  | awk -F= '/^programs:/{print$2}' | \