add dollar sign as valid suffix token

text/2603-rust-symbol-name-mangling-v0.md

@@ -749,8 +749,8 @@ Mangled names conform to the following grammar:
 <instantiating-crate> = <path>
 
 // There are no restrictions on the characters that may be used
-// in the suffix following the `.`.
-<vendor-specific-suffix> = "." <suffix>
+// in the suffix following the `.` or `$`.
+<vendor-specific-suffix> = ("." | "$") <suffix>
 ```
 
 ### Namespace Tags
@@ -809,12 +809,13 @@ like regular identifiers and need no further special handling.
 ### Vendor-specific suffix
 
 Similarly to the [Itanium C++ ABI mangling scheme][itanium-mangling-structure], a symbol name
-containing a period (`.`) represents a vendor-specific version of the symbol. There are no
-restrictions on the characters following the period.
+containing a period (`.`) or a dollar sign (`$`) represents a vendor-specific version of the symbol.
+There are no restrictions on the characters following the period or dollar sign.
 
 This can happen in practice when locally unique names needed to become globally unique. For example,
-LLVM can append a `.llvm.<numbers>` suffix during LTO to ensure a unique name. In these situations
-it's generally fine to ignore the suffix: the suffixed name has the same semantics as the original.
+LLVM can append a `.llvm.<numbers>` suffix during LTO to ensure a unique name, and `$` can be used
+for thread-local data on Mach-O. In these situations it's generally fine to ignore the suffix: the
+suffixed name has the same semantics as the original.
 
 [itanium-mangling-structure]: https://itanium-cxx-abi.github.io/cxx-abi/abi.html#mangling-structure