Remapper: make remapper robust against non-exiting error handlers

Remapper errors are generally fatal: there has been some unexpected situation while
parsing the SPV binary, and there is no reasonable way to carry on.  The
errorHandler() function is called in this case, which by default exits, but
it is possible to submit a handler which does not.  In that case the remapper would
carry on in a bad state.

This change ensures a graceful termination of the remap() function.

While a try {} catch {} construct would be the ideal and safe way to do this,
that's off limits for certain environments, so this tries to do the same thing
with explicit code, to catch all the bailout paths.

SPIRV/SPVRemapper.h

@@ -39,6 +39,7 @@
 #include <string>
 #include <vector>
 #include <cstdlib>
+#include <exception>
 
 namespace spv {
 
@@ -111,7 +112,9 @@ namespace spv {
 class spirvbin_t : public spirvbin_base_t
 {
 public:
-   spirvbin_t(int verbose = 0) : entryPoint(spv::NoResult), largestNewId(0), verbose(verbose) { }
+   spirvbin_t(int verbose = 0) : entryPoint(spv::NoResult), largestNewId(0), verbose(verbose), errorLatch(false)
+   { }
+
    virtual ~spirvbin_t() { }
 
    // remap on an existing binary in memory
@@ -165,7 +168,7 @@ private:
    typedef std::unordered_map<spv::Id, unsigned> typesize_map_t;
 
    // handle error
-   void error(const std::string& txt) const { errorHandler(txt); }
+   void error(const std::string& txt) const { errorLatch = true; errorHandler(txt); }
 
    bool     isConstOp(spv::Op opCode)      const;
    bool     isTypeOp(spv::Op opCode)       const;
@@ -286,6 +289,11 @@ private:
    std::uint32_t options;
    int           verbose;     // verbosity level
 
+   // Error latch: this is set if the error handler is ever executed.  It would be better to
+   // use a try/catch block and throw, but that's not desired for certain environments, so
+   // this is the alternative.
+   mutable bool errorLatch;
+
    static errorfn_t errorHandler;
    static logfn_t   logHandler;
 };