Add Travis builds with sanitizers

This triggers 5 independent build / test runs:
 - clang, no sanitizer;
 - clang, UB sanitizer;
 - clang, address sanitizer (disabled for now);
 - clang, thread sanitizer (disabled for now);
 - GCC.

Enabling UBSan led to these changes:
 - Fix a bunch of undefined behavior throughout the code base.
 - Fix some tests that relied on that undefined behavior.
 - Make some of the tests easier to debug by printing their command line.
 - Add ubsan blacklist to work around libstdc++ bug.
 - Example testcase also needs sanitizer because libsupport.a uses it.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/wasm.h b/src/wasm.h
index b1b8d84d4..c4654580a 100644
--- a/src/wasm.h
+++ b/src/wasm.h
@@ -45,13 +45,14 @@
 #define wasm_wasm_h
 
 #include <cassert>
+#include <cmath>
 #include <cstddef>
 #include <cstdint>
 #include <cstring>
 #include <fstream>
 #include <map>
-#include <vector>
 #include <string>
+#include <vector>
 
 #include "compiler-support.h"
 #include "emscripten-optimizer/simple_ast.h"
@@ -200,7 +201,7 @@ struct Literal {
   }
 
   static void printDouble(std::ostream &o, double d) {
-    if (d == 0 && 1/d < 0) {
+    if (d == 0 && std::signbit(d)) {
       o << "-0";
       return;
     }