[diff.mods.to.headers] Cover type-generic macro suppression

Author: hubert-reinterpretcast

source/compatibility.tex

@@ -3720,7 +3720,9 @@
 The C headers \libheader{complex.h} and
 \libheader{tgmath.h} do not contain any of the content from
 the C standard library and instead merely include other headers from the \Cpp{}
-standard library.
+standard library. Whereas the \libheader{tgmath.h} macros can be suppressed in
+C by, for example, using parentheses around the macro name, the \Cpp{} overload
+sets cannot be bypassed in this manner; casts may be used instead.
 
 \rSec2[diff.mods.to.definitions]{Modifications to definitions}