Add documentation for indirect branch tracking flags (#796)

These flags were added in crystal-lang/crystal#15122

They are put in a new section *Codegen Features*. The existing *Compiler Features* section is renamed to *Language Features*.

docs/man/required_libraries.md

@@ -68,7 +68,7 @@ Using a standalone library over the system library implementation can be enforce
 
 ### TLS
 
-TLS protocol implementation and general-purpose cryptographic routines for the [`OpenSSL`](https://crystal-lang.org/api/OpenSSL.html) API. May be disabled with the `-Dwithout_openssl` [compile-time flag](../syntax_and_semantics/compile_time_flags.md#compiler-features).
+TLS protocol implementation and general-purpose cryptographic routines for the [`OpenSSL`](https://crystal-lang.org/api/OpenSSL.html) API. May be disabled with the `-Dwithout_openssl` [compile-time flag](../syntax_and_semantics/compile_time_flags.md#stdlib-features).
 
 Both `OpenSSL` and `LibreSSL` are supported and the bindings automatically detect which library and API version is available on the host system.
 

docs/syntax_and_semantics/autocasting.md

@@ -27,7 +27,7 @@ bar64(bar 1)   # OK, a Float32 can be autocasted to a Float64
 
 Number literals are always casted when the actual value of the literal fits the target type, despite of its type.
 
-Expressions are casted (like in the last example above), unless the flag `no_number_autocast` is passed to the compiler (see [Compiler features](compile_time_flags.md#compiler-features)).
+Expressions are casted (like in the last example above), unless the flag `no_number_autocast` is passed to the compiler (see [Compiler features](compile_time_flags.md#language-features)).
 
 If there is ambiguity, for instance, because there is more than one option, the compiler throws an error:
 

docs/syntax_and_semantics/compile_time_flags.md

@@ -145,9 +145,9 @@ Crystal program.
 | `without_openssl` | Build without OpenSSL support
 | `without_zlib` | Build without Zlib support
 
-### Compiler features
+### Language features
 
-These flags enable or disable compiler features when building a Crystal program.
+These flags enable or disable language features when building a Crystal program.
 
 | Flag name | Description |
 |-----------|-------------|
@@ -156,6 +156,15 @@ These flags enable or disable compiler features when building a Crystal program.
 | `preview_overload_order` | Enable more robust ordering between def overloads. Introduced in 1.6 ([#10711](https://github.com/crystal-lang/crystal/issues/10711)).
 | `strict_multi_assign` | Enable strict semantics for [one-to-many assignment](assignment.md#one-to-many-assignment). Introduced in 1.3.0 ([#11145](https://github.com/crystal-lang/crystal/pull/11145), [#11545](https://github.com/crystal-lang/crystal/pull/11545))
 
+### Codegen features
+
+These flags enable or disable codegen features when building a Crystal program.
+
+| Flag name | Description |
+|-----------|-------------|
+| `cf-protection=branch`, `cf-protection=return`, `cf-protection=full` | Indirect branch tracking for x86 and x86_64. Implicitly set on OpenBSD. Introduced in 1.15.0 ([#15122](https://github.com/crystal-lang/crystal/pull/15122))
+| `branch-protection=bti` | Indirect branch tracking for aarch64. Implicitly set on OpenBSD. Introduced in 1.15.0 ([#15122](https://github.com/crystal-lang/crystal/pull/15122))
+
 ### Compiler build features
 
 These flags enable or disable features when building the Crystal compiler.