build: fix fmt throwing behavior warnings (#4730)

Certain version combinations of fmt and gcc were warning, and it all
boiled down to the knots we tied ourselves into to replace the function
fmt uses instead of throwing exceptions, when they are disabled. I can't
seem to find any harm in letting it do its default thing, so simplify
our side to silence the warnings.

Signed-off-by: Larry Gritz <lg@larrygritz.com>

Author: lgritz

src/include/OpenImageIO/detail/fmt.h

@@ -19,18 +19,14 @@
 #    define FMT_EXCEPTIONS 0
 #endif
 
+#if OIIO_VERSION_LESS(3, 1, 2)
+/* DEPRECATED -- remove at next ABI compatibility boundary */
 OIIO_NAMESPACE_BEGIN
 namespace pvt {
 OIIO_UTIL_API void
 log_fmt_error(const char* message);
 };
 OIIO_NAMESPACE_END
-
-// Redefining FMT_THROW to print and log the error. This should only occur if
-// we've made a mistake and mismatched a format string and its arguments.
-// Hopefully this will help us track it down.
-#if !defined(FMT_THROW) && !FMT_EXCEPTIONS
-#    define FMT_THROW(x) OIIO::pvt::log_fmt_error((x).what())
 #endif
 
 // Use the grisu fast floating point formatting for old fmt versions
@@ -67,12 +63,6 @@ OIIO_PRAGMA_WARNING_PUSH
 #if OIIO_CLANG_VERSION >= 180000
 #    pragma clang diagnostic ignored "-Wdeprecated-declarations"
 #endif
-#if OIIO_CLANG_VERSION || OIIO_APPLE_CLANG_VERSION
-#    pragma clang diagnostic ignored "-Winvalid-noreturn"
-#endif
-// #if OIIO_GNUC_VERSION
-// #    pragma gcc diagnostic ignored "-Winvalid-noreturn"
-// #endif
 
 #include <OpenImageIO/detail/fmt/format.h>
 #include <OpenImageIO/detail/fmt/ostream.h>

src/libutil/strutil.cpp

@@ -246,12 +246,14 @@ Strutil::pvt::geterror(bool clear)
 }
 
 
+#if OIIO_VERSION_LESS(3, 1, 2) /* remove at next ABI compatibility boundary */
 void
 pvt::log_fmt_error(const char* message)
 {
     print("fmt exception: {}\n", message);
     Strutil::pvt::append_error(std::string("fmt exception: ") + message);
 }
+#endif