Rollup merge of rust-lang#149154 - apiraino:fix-platform-support-typo, r=lqd

Fix platform supports docs tiny typo

This was noticed in rust-lang/blog.rust-lang.org#1641 (comment)

Thanks :)

Author: matthiaskrgr

src/doc/rustc/src/platform-support.md

@@ -182,7 +182,7 @@ target | std | notes
 [`riscv32imac-unknown-none-elf`](platform-support/riscv32-unknown-none-elf.md) | * | Bare RISC-V (RV32IMAC ISA)
 [`riscv32imafc-unknown-none-elf`](platform-support/riscv32-unknown-none-elf.md) | * | Bare RISC-V (RV32IMAFC ISA)
 [`riscv32imc-unknown-none-elf`](platform-support/riscv32-unknown-none-elf.md) | * | Bare RISC-V (RV32IMC ISA)
-[`riscv64gc-unknown-linux-musl`](platform-support/riscv64gc-unknown-linux-musl.md) | RISC-V Linux (kernel 4.20+, musl 1.2.5)
+[`riscv64gc-unknown-linux-musl`](platform-support/riscv64gc-unknown-linux-musl.md) | ✓ |RISC-V Linux (kernel 4.20+, musl 1.2.5)
 `riscv64gc-unknown-none-elf` | * | Bare RISC-V (RV64IMAFDC ISA)
 `riscv64imac-unknown-none-elf` | * | Bare RISC-V (RV64IMAC ISA)
 `sparc64-unknown-linux-gnu` | ✓ | SPARC Linux (kernel 4.4+, glibc 2.23)