Implement malloc_vsnprintf().

Implement malloc_vsnprintf() (a subset of vsnprintf(3)) as well as
several other printing functions based on it, so that formatted printing
can be relied upon without concern for inducing a dependency on floating
point runtime support.  Replace malloc_write() calls with
malloc_*printf() where doing so simplifies the code.

Add name mangling for library-private symbols in the data and BSS
sections.  Adjust CONF_HANDLE_*() macros in malloc_conf_init() to expose
all opt_* variable use to cpp so that proper mangling occurs.

configure.ac

@@ -144,6 +144,18 @@ else
 fi
 AC_DEFINE_UNQUOTED([LG_SIZEOF_LONG], [$LG_SIZEOF_LONG])
 
+AC_CHECK_SIZEOF([intmax_t])
+if test "x${ac_cv_sizeof_intmax_t}" = "x16" ; then
+  LG_SIZEOF_INTMAX_T=4
+elif test "x${ac_cv_sizeof_intmax_t}" = "x8" ; then
+  LG_SIZEOF_INTMAX_T=3
+elif test "x${ac_cv_sizeof_intmax_t}" = "x4" ; then
+  LG_SIZEOF_INTMAX_T=2
+else
+  AC_MSG_ERROR([Unsupported intmax_t size: ${ac_cv_sizeof_long}])
+fi
+AC_DEFINE_UNQUOTED([LG_SIZEOF_INTMAX_T], [$LG_SIZEOF_INTMAX_T])
+
 AC_CANONICAL_HOST
 dnl CPU-specific settings.
 CPU_SPINWAIT=""