[C++] Make code compile with -Wfloat-equal (#8221)

This will allow the code to be compiled with `-Wfloat-equal`
as this would result in the folowing warning/error:
vendor/flatbuffers/include/flatbuffers/base.h:465:69:
  error: comparing floating point with == or != is unsafe [-Werror,-Wfloat-equal]
template<typename T> inline bool IsTheSameAs(T e, T def) { return e == def; }

But the way it is used in flatbuffers it is ok to compare floating
points with ==.

Co-authored-by: Derek Bailey <derekbailey@google.com>

include/flatbuffers/base.h

@@ -459,10 +459,17 @@ inline size_t PaddingBytes(size_t buf_size, size_t scalar_size) {
   return ((~buf_size) + 1) & (scalar_size - 1);
 }
 
+#if !defined(_MSC_VER)
+  #pragma GCC diagnostic push
+  #pragma GCC diagnostic ignored "-Wfloat-equal"
+#endif
 // Generic 'operator==' with conditional specialisations.
 // T e - new value of a scalar field.
 // T def - default of scalar (is known at compile-time).
 template<typename T> inline bool IsTheSameAs(T e, T def) { return e == def; }
+#if !defined(_MSC_VER)
+  #pragma GCC diagnostic pop
+#endif
 
 #if defined(FLATBUFFERS_NAN_DEFAULTS) && \
     defined(FLATBUFFERS_HAS_NEW_STRTOD) && (FLATBUFFERS_HAS_NEW_STRTOD > 0)