audit_symbols: Allow Windows RTTI descriptors to be unprefixed

On Windows, if A subclasses B and A has a vtable, Windows will emit RTTI
descriptors for B. This happens even if B is a trivial type, which
breaks our type name strategy. Fortunately, these RTTI descriptors only
describe B's inheritance structure, which we can reasonably assume is
trivial, so it is OK if they are unprefixed.

Suppress those symbols for now. It's not amazing, but is probably fine.
If it breaks later, we can always reach for /GS- or so.

Some notes on C++ name mangling in MSVC for reference:
https://en.wikiversity.org/wiki/Visual_C%2B%2B_name_mangling#Special_Name

Bug: 42220000
Change-Id: I2885b5068de80b61d575c6cb6439907d86f01a1a
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/89967
Reviewed-by: Rudolf Polzer <rpolzer@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
Auto-Submit: David Benjamin <davidben@google.com>

util/audit_symbols.go

diff --git a/util/audit_symbols.go b/util/audit_symbols.go
index ccb63e0..3691814 100644
--- a/util/audit_symbols.go
+++ b/util/audit_symbols.go
@@ -85,6 +85,7 @@
 	regexp.MustCompile(`^fprintf$`),                                     // fprintf()
 	regexp.MustCompile(`^snprintf$`),                                    // snprintf()
 	regexp.MustCompile(`^vsnprintf$`),                                   // vsnprintf()
+	regexp.MustCompile(`^\?\?_R[0-4].*$`),                               // RTTI
 
 	// Symbols in the FIPS module.
 	// They are provided for tooling only and should not be read internally.