Add more ABI correspondence with other compilers

Author: ehuss

src/items/external-blocks.md

@@ -131,13 +131,15 @@ There are also some platform-specific ABI strings:
 r[items.extern.abi.cdecl]
 * `unsafe extern "cdecl"` --- The calling convention typically used with x86_32 C code.
   * Only available on x86_32 targets.
+  * Corresponds to MSVC's `__cdecl` and GCC and clang's `__attribute__((cdecl))`.
 
   > [!NOTE]
   > See <https://learn.microsoft.com/en-us/cpp/cpp/cdecl> and <https://en.wikipedia.org/wiki/X86_calling_conventions#cdecl> for more information.
 
 r[items.extern.abi.stdcall]
 * `unsafe extern "stdcall"` --- The calling convention typically used by the [Win32 API] on x86_32.
   * Only available on x86_32 targets.
+  * Corresponds to MSVC's `__stdcall` and GCC and clang's `__attribute__((stdcall))`.
 
   > [!NOTE]
   > See <https://learn.microsoft.com/en-us/cpp/cpp/stdcall> and <https://en.wikipedia.org/wiki/X86_calling_conventions#stdcall> for more information.
@@ -146,6 +148,7 @@ r[items.extern.abi.win64]
 * `unsafe extern "win64"` --- The Windows x64 ABI.
   * Only available on x86_64 targets.
   * "win64" is the same as the "C" ABI on Windows x86_64 targets.
+  * Corresponds to GCC and clang's `__attribute__((ms_abi))`.
 
   > [!NOTE]
   > See <https://learn.microsoft.com/en-us/cpp/build/x64-software-conventions> and <https://en.wikipedia.org/wiki/X86_calling_conventions#Microsoft_x64_calling_convention> for more information.
@@ -154,6 +157,7 @@ r[items.extern.abi.sysv64]
 * `unsafe extern "sysv64"` --- The System V ABI.
   * Only available on x86_64 targets.
   * "sysv64" is the same as the "C" ABI on non-Windows x86_64 targets.
+  * Corresponds to GCC and clang's `__attribute__((sysv_abi))`.
 
   > [!NOTE]
   > See <https://wiki.osdev.org/System_V_ABI> or <https://en.wikipedia.org/wiki/X86_calling_conventions#System_V_AMD64_ABI> for more information.
@@ -162,20 +166,23 @@ r[items.extern.abi.aapcs]
 * `unsafe extern "aapcs"` --- The soft-float ABI for ARM.
   * Only available on ARM32 targets.
   * "aapcs" is the same as the "C" ABI on soft-float ARM32.
+  * Corresponds to clang's `__attribute__((pcs("aapcs")))`.
 
   > [!NOTE]
   > See [Arm Procedure Call Standard](https://developer.arm.com/documentation/107656/0101/Getting-started-with-Armv8-M-based-systems/Procedure-Call-Standard-for-Arm-Architecture--AAPCS-) for more information.
 
 r[items.extern.abi.fastcall]
-* `unsafe extern "fastcall"` --- The `fastcall` ABI --- corresponds to MSVC's `__fastcall` and GCC and clang's `__attribute__((fastcall))`.
+* `unsafe extern "fastcall"` --- A "fast" variant of stdcall that passes some arguments in registers.
   * Only available on x86_32 targets.
+  * Corresponds to MSVC's `__fastcall` and GCC and clang's `__attribute__((fastcall))`.
 
   > [!NOTE]
   > See <https://learn.microsoft.com/en-us/cpp/cpp/fastcall> and <https://en.wikipedia.org/wiki/X86_calling_conventions#Microsoft_fastcall> for more information.
 
 r[items.extern.abi.thiscall]
-* `unsafe extern "thiscall"` --- The calling convention typically used on C++ class member functions on x86_32 MSVC --- corresponds to MSVC's `__thiscall` and GCC and clang's `__attribute__((thiscall))`.
+* `unsafe extern "thiscall"` --- The calling convention typically used on C++ class member functions on x86_32 MSVC.
   * Only available on x86_32 targets.
+  * Corresponds to MSVC's `__thiscall` and GCC and clang's `__attribute__((thiscall))`.
 
   > [!NOTE]
   > See <https://en.wikipedia.org/wiki/X86_calling_conventions#thiscall> and <https://learn.microsoft.com/en-us/cpp/cpp/thiscall> for more information.