[libc] Fix constant address space on global clock

Summary:
I did this wrong in the first version, because `extern "C"` doesn't
imply it's extern when used directly.

Author: jhuber6

libc/src/time/gpu/time_utils.cpp

@@ -15,8 +15,7 @@ namespace LIBC_NAMESPACE {
 // insufficient.
 // TODO: Once we have another use-case for this we should put it in a common
 // device environment struct.
-extern "C" [[gnu::visibility("protected")]] uint64_t __llvm_libc_clock_freq =
-    clock_freq;
+gpu::Constant<uint64_t> __llvm_libc_clock_freq = clock_freq;
 #endif
 
 } // namespace LIBC_NAMESPACE

libc/src/time/gpu/time_utils.h

@@ -23,7 +23,10 @@ constexpr uint64_t clock_freq = 100000000UL;
 
 // We provide an externally visible symbol such that the runtime can set
 // this to the correct value.
-extern "C" [[gnu::visibility("protected")]] uint64_t __llvm_libc_clock_freq;
+extern "C" {
+[[gnu::visibility("protected")]]
+extern gpu::Constant<uint64_t> __llvm_libc_clock_freq;
+}
 #define GPU_CLOCKS_PER_SEC static_cast<clock_t>(__llvm_libc_clock_freq)
 
 #elif defined(LIBC_TARGET_ARCH_IS_NVPTX)