BareMetal: Add support for RISC-V architecture in GCC toolchain

This commit adds support for the RISC-V atchitecture:

 * https://riscv.org/

using GCC toolchains.

Tested auto-detection on Windows using the GCC v7.7.1 toolchain
provided from the following URL:

 * https://gnutoolchains.com/risc-v/

Change-Id: Ice10469ebda8af9cf7bf32299bb38e548b30b315
Reviewed-by: hjk <hjk@qt.io>

src/plugins/projectexplorer/abi.cpp

@@ -517,6 +517,12 @@ Abi Abi::abiFromTargetTriplet(const QString &triple)
             flavor = GenericFlavor;
             format = ElfFormat;
             width = 32;
+        } else if (p.startsWith("riscv")) {
+            arch = RiscVArchitecture;
+            os = BareMetalOS;
+            flavor = GenericFlavor;
+            format = ElfFormat;
+            width = 32;
         } else if (p.startsWith("mips")) {
             arch = MipsArchitecture;
             width = p.contains("64") ? 64 : 32;