add riscv64 as supported architecture on linux

Author: futurejones

utils/build-script-impl

@@ -465,6 +465,7 @@ function verify_host_is_supported() {
       | linux-powerpc           \
       | linux-powerpc64         \
       | linux-powerpc64le       \
+      | linux-riscv64           \
       | linux-s390x             \
       | macosx-x86_64           \
       | macosx-arm64            \

utils/swift_build_support/swift_build_support/targets.py

@@ -275,6 +275,7 @@ class StdlibDeploymentTarget(object):
         "powerpc",
         "powerpc64",
         "powerpc64le",
+        "riscv64",
         "s390x"])
 
     FreeBSD = Platform("freebsd", archs=["x86_64"])
@@ -361,6 +362,8 @@ def host_target():
                 return StdlibDeploymentTarget.Linux.powerpc64
             elif machine == 'ppc64le':
                 return StdlibDeploymentTarget.Linux.powerpc64le
+            elif machine == 'riscv64':
+                return StdlibDeploymentTarget.Linux.riscv64
             elif machine == 's390x':
                 return StdlibDeploymentTarget.Linux.s390x