[libcxx][test] Update picolibc version (#100348)

This is the latest as of today, and it fixes one of the xfails.

Since
picolibc/picolibc@5e4d0c8,
TIME_UTC is defined.

Author: DavidSpickett

libcxx/test/std/language.support/support.runtime/ctime.timespec.compile.pass.cpp

@@ -11,9 +11,6 @@
 
 // UNSUPPORTED: c++03, c++11, c++14
 
-// picolibc doesn't define TIME_UTC.
-// XFAIL: LIBCXX-PICOLIBC-FIXME
-
 // ::timespec_get is provided by the C library, but it's marked as
 // unavailable until macOS 10.15
 // XFAIL: target={{.+}}-apple-macosx10.{{13|14}}

libcxx/utils/ci/build-picolibc.sh

@@ -69,13 +69,8 @@ picolibc_source_dir="${build_dir}/picolibc-source"
 picolibc_build_dir="${build_dir}/picolibc-build"
 mkdir -p "${picolibc_source_dir}"
 mkdir -p "${picolibc_build_dir}"
-# Download the version of picolibc that was the latest at the time this script was written.
-# Following changes are required and were introduced after version 1.8.5:
-# - updated semihost arguments handling,
-# - added missing macros in stdio.h
-# - external linkage for isblank
-# Version following 1.8.5, was not released by the time of writing.
-picolibc_commit="04a90c56d7aac61880f205ec29b3dce6a9de0342"
+# Download a known good version of picolibc.
+picolibc_commit="48fbc2009c6473293d03d5ec6f190565c6223a5c"
 curl -L "https://github.com/picolibc/picolibc/archive/${picolibc_commit}.zip" --output "${picolibc_source_dir}/picolibc.zip"
 unzip -q "${picolibc_source_dir}/picolibc.zip" -d "${picolibc_source_dir}"
 mv "${picolibc_source_dir}/picolibc-${picolibc_commit}"/* "${picolibc_source_dir}"