Use the libc++ detection instead of clang detection around std:isinfinite (#52164)

Summary:
Fixes #52163

The libc++ vs libstdc++ detection in the pre-processor is taken from https://stackoverflow.com/questions/31657499/how-to-detect-stdlib-libc-in-the-preprocessor

Note that in our case `std:isinfinite` presents means that we don't need to import any additional headers to guarantee the `_LIBCPP_VERSION` presents for the `libc++`.

Pull Request resolved: #52164

Reviewed By: albanD

Differential Revision: D26413108

Pulled By: malfet

fbshipit-source-id: 515e258d6758222c910ababf5172c3a275aff08f

Author: vors

aten/src/ATen/native/cpu/MultinomialKernel.cpp

@@ -47,9 +47,9 @@ void multinomial_with_replacement_apply(
     for (int64_t j = 0; j < n_categories; j++) {
       val = self_ptr[i * self_stride_0 + j * self_stride_1];
       TORCH_CHECK(val >= 0, "invalid multinomial distribution (encountering probability entry < 0)");
-// NB: std::isfinite doesn't bode well with clang for half datatypes,
+// NB: std::isfinite doesn't bode well with libc++ for half datatypes,
 // so we manually cast it to a double and perform the check.
-#if defined(__clang__)
+#if defined(_LIBCPP_VERSION)
       TORCH_CHECK(std::isfinite(static_cast<double>(val)),
                   "invalid multinomial distribution (encountering probability entry = infinity or NaN)");
 #else