Add UBSAN build option and fix undefined behaviour errors.

Makefile.standalone

 # The following variables will likely need to be modified, depending on where
 # and how you built LLVM & Clang. They can be overridden in a command-line
 # invocation of make, like:
 #
 #   make LLVM_SRC_PATH=<path> LIBCXX_INSTALL_PATH=<path> CLANG_PATH=<path> \
 #        PNACL_BIN_PATH=<path> ...
 #
 
 # LLVM_SRC_PATH is the path to the root of the checked out source code. This
 # directory should contain the configure script, the include/ and lib/
@@ skipping 78 matching lines @@
 SB_CXX_DEFINES := $(BASE_CXX_DEFINES) -DPNACL_BROWSER_TRANSLATOR=1
 CXX_DEFINES := $(BASE_CXX_DEFINES) -DPNACL_BROWSER_TRANSLATOR=0
 
 ifdef NOASSERT
   ASSERTIONS = -DNDEBUG
 else
   ASSERTIONS =
   OBJDIR := $(OBJDIR)+Asserts
 endif
 
+ifdef UBSAN
+  OBJDIR := $(OBJDIR)+UBSan
+  CXX_EXTRA += -fsanitize=undefined -fno-sanitize=vptr
+  LD_EXTRA += -fsanitize=undefined
+endif
+
 ifdef TSAN
   OBJDIR := $(OBJDIR)+TSan
   CXX_EXTRA += -fsanitize=thread
   LD_EXTRA += -fsanitize=thread
 endif
 
 ifdef ASAN
   OBJDIR := $(OBJDIR)+ASan
   CXX_EXTRA += -fsanitize=address
   LD_EXTRA += -fsanitize=address
@@ skipping 289 matching lines @@
 
 docs:
         doxygen Doxyfile
         @echo See file://`pwd`/docs/html/index.html
 
 clean:
         rm -rf pnacl-sz *.o $(OBJDIR) $(SB_OBJDIR) build/pnacl-sz.bloat.json
 
 clean-all: clean
         rm -rf build/ docs/