Remove the usage of UBSAN

Address issue #113. Use of UBSAN in runtime could introduce
vulnerabilities.

Original bug report:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1031744

Reference:
https://www.openwall.com/lists/oss-security/2016/02/17/9

Makefile

@@ -1,7 +1,7 @@
 VERSION = 1.2.4
 
 CFLAGS += -g -O2  -Wall -Wextra -Wshadow \
-	-fsanitize=undefined -fanalyzer -Wno-analyzer-file-leak \
+	-fanalyzer -Wno-analyzer-file-leak \
 	-rdynamic -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -DVERSION=\"$(VERSION)\"\
 	`pkg-config --cflags-only-I gumbo libcurl fuse uuid expat`
 LDFLAGS += `pkg-config --libs-only-L gumbo libcurl fuse uuid expat`