Build LLVM with RISCV support

Author: colemancda

utils/build-presets.ini

@@ -857,6 +857,7 @@ relocate-xdg-cache-home-under-build-subdir
 mixin-preset=
     mixin_linux_installation
 build-subdir=buildbot_linux
+llvm-targets-to-build=X86;ARM;AArch64;PowerPC;SystemZ;Mips;RISCV
 lldb
 release
 test
@@ -1472,7 +1473,7 @@ mixin-preset=
 [preset: LLDB_Nested]
 skip-build-benchmarks
 install-destdir=%(swift_install_destdir)s
-llvm-targets-to-build=X86;ARM;AArch64;PowerPC;SystemZ;Mips
+llvm-targets-to-build=X86;ARM;AArch64;PowerPC;SystemZ;Mips;RISCV
 
 [preset: LLDB_Swift_DebugAssert]
 mixin-preset=