[libc] Bump up minimum PTX version to 6.3

Summary:
I neglected the fact that `activemask` is a 6.2 or 6.3 feature, so
building this on older machines is incorrect. Bump this up to 6.3 for
now so it works. In the future we will try to get rid of the N
architecture business.

libc/cmake/modules/LLVMLibCObjectRules.cmake

@@ -106,13 +106,13 @@ function(get_nvptx_compile_options output_var gpu_arch)
   list(APPEND nvptx_options "-Wno-unknown-cuda-version")
   list(APPEND nvptx_options "SHELL:-mllvm -nvptx-emit-init-fini-kernel=false")
   if(${gpu_arch} STREQUAL "sm_35")
-    list(APPEND nvptx_options "--cuda-feature=+ptx60")
+    list(APPEND nvptx_options "--cuda-feature=+ptx63")
   elseif(${gpu_arch} STREQUAL "sm_37")
-    list(APPEND nvptx_options "--cuda-feature=+ptx60")
+    list(APPEND nvptx_options "--cuda-feature=+ptx63")
   elseif(${gpu_arch} STREQUAL "sm_50")
-    list(APPEND nvptx_options "--cuda-feature=+ptx60")
+    list(APPEND nvptx_options "--cuda-feature=+ptx63")
   elseif(${gpu_arch} STREQUAL "sm_52")
-    list(APPEND nvptx_options "--cuda-feature=+ptx60")
+    list(APPEND nvptx_options "--cuda-feature=+ptx63")
   elseif(${gpu_arch} STREQUAL "sm_53")
     list(APPEND nvptx_options "--cuda-feature=+ptx63")
   elseif(${gpu_arch} STREQUAL "sm_60")