Add a possible justification for the multiarch specifier change.

For the record: this is DEFINITELY NOT the full reason behind the
closed-door decision. But this is about as close as we community people
can get in persuading the depressed ourselves, and about all I can
disclose after having multiple private conversations with relevant
parties, without inflicting damage to Loongson unwanted by me and all.

docs/LoongArch-toolchain-conventions-CN.adoc

@@ -293,6 +293,8 @@ ABI 配置的需要。若不能，则应根据下表，在默认可用指令集
 本《约定》的 1.00 版本曾规定了基础 ABI 使用 64 位浮点寄存器传参时的
 `<fabi_suffix>` 后缀为 `f64` （意味着类似 `loongarch64-linux-gnuf64` 的
 multiarch 架构标识符取值）。
+2.00 版本起将其改为空字符串，是考虑到最常见的组合适合尽量短的名字，
+因此不介意文本上的不兼容变更。
 为尽可能维持向后兼容，应在见到 `gnuf64` 这一目标元组环境字段取值时，
 将其视为（标准化为） `gnu` 如果这样做因不会带来其他超越近处业务逻辑的外部副作用而可行。
 （例如：如果维持对 `gnuf64` 的兼容性涉及必须添加符号链接或复制文件，

docs/LoongArch-toolchain-conventions-EN.adoc

@@ -334,6 +334,9 @@ specifier, respectively.
 Version 1.00 of this document mandated that a `<fabi-suffix>` of `f64` shall
 be used for cases where the base ABI used 64-bit FPRs for parameter passing
 (meaning multiarch architecture specifier values resembling `loongarch64-linux-gnuf64`).
+From version 2.00 onwards it was changed into the empty string;
+the incompatible textual change is justified by the rationale that shorter
+names are preferred for the more ubiquitous combinations.
 For maintaining best-effort backwards compatibility, the target tuple environment
 value `gnuf64` shall be treated as (canonicalized into) `gnu` if doing so
 would be feasible by not bringing any external side effects that goes beyond