Cleanup warnings with nvhpc/21.9. (#2582)

* Cleanup warnings with nvhpc/21.9.

* Move __NVCOMPILER check.

* Be more explicit.

* Immediately executed lambda.

* Fix shadowing warning.

include/fmt/core.h

@@ -24,7 +24,8 @@
 #  define FMT_CLANG_VERSION 0
 #endif
 
-#if defined(__GNUC__) && !defined(__clang__) && !defined(__INTEL_COMPILER)
+#if defined(__GNUC__) && !defined(__clang__) && !defined(__INTEL_COMPILER) && \
+    !defined(__NVCOMPILER)
 #  define FMT_GCC_VERSION (__GNUC__ * 100 + __GNUC_MINOR__)
 #else
 #  define FMT_GCC_VERSION 0

include/fmt/format.h

@@ -970,11 +970,14 @@ FMT_CONSTEXPR auto count_digits(UInt n) -> int {
   if (num_bits<UInt>() == 32)
     return (FMT_BUILTIN_CLZ(static_cast<uint32_t>(n) | 1) ^ 31) / BITS + 1;
 #endif
-  int num_digits = 0;
-  do {
-    ++num_digits;
-  } while ((n >>= BITS) != 0);
-  return num_digits;
+  // Lambda avoids unreachable code warnings from NVHPC.
+  return [](UInt m) {
+    int num_digits = 0;
+    do {
+      ++num_digits;
+    } while ((m >>= BITS) != 0);
+    return num_digits;
+  }(n);
 }
 
 template <> auto count_digits<4>(detail::fallback_uintptr n) -> int;