Interpret x86_64 as x86-64 for architecture

CMakeLists.txt

@@ -211,7 +211,11 @@ else()
   if(ARCH STREQUAL "default")
     set(ARCH_FLAG "")
   else()
-    set(ARCH_FLAG "-march=${ARCH}")
+    if(ARCH STREQUAL "x86_64")
+      set(ARCH_FLAG "-march=x86-64")
+    else()
+      set(ARCH_FLAG "-march=${ARCH}")
+    endif()
   endif()
   set(WARNINGS "-Wall -Wextra -Wpointer-arith -Wundef -Wvla -Wwrite-strings -Wno-error=extra -Wno-error=deprecated-declarations -Wno-error=sign-compare -Wno-error=strict-aliasing -Wno-error=type-limits -Wno-unused-parameter -Wno-error=unused-variable -Wno-error=undef -Wno-error=uninitialized")
   if(CMAKE_C_COMPILER_ID STREQUAL "Clang")