build: allow riscv64

Author: Theo Paris

CMakeLists.txt

@@ -19,6 +19,8 @@ elseif(${OPENLIBM_ARCH_FOLDER} STREQUAL "x86")
     set(OPENLIBM_ARCH_FOLDER "i387")
 elseif(${OPENLIBM_ARCH_FOLDER} STREQUAL "powerpc")
     set(OPENLIBM_ARCH_FOLDER "powerpc")
+elseif(${OPENLIBM_ARCH_FOLDER} STREQUAL "riscv64")
+    set(OPENLIBM_ARCH_FOLDER "riscv64")
 else()
     message(FATAL_ERROR "${PROJECT_NAME} not set up for detected architecture: ${OPENLIBM_ARCH_FOLDER}")
 endif()