Merge pull request #202 from Disasm/add-riscv

Update platform list: add RISC-V targets

platform-support.md

@@ -83,6 +83,10 @@ these platforms are required to have each of the following:
 | `powerpc-unknown-linux-gnu` | ✓ | ✓ | ✓ | PowerPC Linux |
 | `powerpc64-unknown-linux-gnu` | ✓ | ✓ | ✓ | PPC64 Linux |
 | `powerpc64le-unknown-linux-gnu` | ✓ | ✓ | ✓ | PPC64LE Linux |
+| `riscv32imac-unknown-none-elf` | * | | | Bare RISC-V (RV32IMAC ISA) |
+| `riscv32imc-unknown-none-elf` | * | | | Bare RISC-V (RV32IMC ISA) |
+| `riscv64gc-unknown-none-elf` | * | | | Bare RISC-V (RV64IMAFDC ISA) |
+| `riscv64imac-unknown-none-elf` | * | | | Bare RISC-V (RV64IMAC ISA) |
 | `s390x-unknown-linux-gnu` | ✓ | ✓ | ✓ | S390x Linux |
 | `sparc64-unknown-linux-gnu` | ✓ | | | SPARC Linux |
 | `sparcv9-sun-solaris` | ✓ | | | SPARC Solaris 10/11, illumos |
@@ -103,6 +107,9 @@ these platforms are required to have each of the following:
 
 [Fortanix ABI]: https://edp.fortanix.com
 
+<em>*</em> These are bare-metal microcontroller targets that only have access to
+the core library, not std.
+
 ## Tier 2.5
 
 Tier 2.5 platforms can be thought of as "guaranteed to build", but without