[libcxx] Fix build for glibc < 2.27

PR llvm#109211 introduced a build break on systems with glibc < 2.27, since
copy_file_range was only introduced after that version. A version check
is added to prevent this breakage.

Author: kongy

libcxx/src/filesystem/operations.cpp

@@ -39,8 +39,8 @@
 #include <fcntl.h> /* values for fchmodat */
 #include <time.h>
 
-// since Linux 4.5 and FreeBSD 13, but the Linux libc wrapper is only provided by glibc and musl
-#if (defined(__linux__) && (defined(__GLIBC__) || _LIBCPP_HAS_MUSL_LIBC)) || defined(__FreeBSD__)
+// since Linux 4.5 and FreeBSD 13, but the Linux libc wrapper is only provided by glibc >= 2.27 and musl
+#if (defined(__linux__) && (_LIBCPP_GLIBC_PREREQ(2, 27) || _LIBCPP_HAS_MUSL_LIBC)) || defined(__FreeBSD__)
 #  define _LIBCPP_FILESYSTEM_USE_COPY_FILE_RANGE
 #endif
 #if __has_include(<sys/sendfile.h>)