Update CoverageMapping Format Version requirements

Author: Swatinem

src/llvm-coverage-instrumentation.md

@@ -221,15 +221,15 @@ substitution combinations), `mapgen`'s `finalize()` method queries the
 and `CodeRegion`s; and calls LLVM codegen APIs to generate
 properly-configured variables in LLVM IR, according to very specific
 details of the [_LLVM Coverage Mapping Format_][coverage-mapping-format]
-(Version 4).[^llvm-and-covmap-versions]
+(Version 5).[^llvm-and-covmap-versions]
 
 [^llvm-and-covmap-versions]: The Rust compiler (as of
-January 2021) supports _LLVM Coverage Mapping Format_ Version 4 (the most
+October 2021) supports _LLVM Coverage Mapping Format_ Version 5 (the most
 up-to-date version of the format, at the time of this writing) for improved
 compatibility with other LLVM-based compilers (like _Clang_), and to take
-advantage of some format optimizations. Version 4 was introduced in _LLVM 11_,
-which is currently the default LLVM version for Rust. Note that the Rust
-compiler optionally supports some earlier LLVM versions, prior to _LLVM 11_. If
+advantage of some format optimizations. Version 5 was introduced in _LLVM 12_,
+which is lower than the current default LLVM version for Rust. Note that the Rust
+compiler optionally supports some earlier LLVM versions, prior to _LLVM 12_. If
 `rustc` is configured to use an incompatible version of LLVM, compiling with `-Z
 instrument-coverage` will generate an error message.