[superproject] Roll llvm-project/libc [libc][CMake] Place archives in build/lib/<target-triple>

This patch moves the location of libllvmlibc.a within the build tree to
within ./lib/<target triple>. This more closely matches the behavior of
other runtime builds and allows for clang in the same build tree to
automatically be able to link against llvmlibc since this path is by
default included by the driver.

Also removes the LIBC_BINARY_DIR CMake flag since it isn't used anywhere
in the tree (based on a quick grep).

Reviewed By: phosek

Differential Revision: https://reviews.llvm.org/D151624

GitOrigin-RevId: eaafae43cd35f250609c8019b77deec676baa2ec
Original-Revision: afc5f8464cc088d25e8b0d6005bd18b9f81026b1
Roller-URL: https://ci.chromium.org/b/8779263906094248065
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I4d117b4a4545d3774db639f25555eecb2925f930
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/865878
diff --git a/third_party/llvm-libc/src b/third_party/llvm-libc/src
index 5d49996..afc5f84 160000
--- a/third_party/llvm-libc/src
+++ b/third_party/llvm-libc/src
@@ -1 +1 @@
-Subproject commit 5d499967a0d9b1591ab0a5e15760d22771f0e7de
+Subproject commit afc5f8464cc088d25e8b0d6005bd18b9f81026b1