glibc: improved to help building/installing correct glibc headers at toolchain stage when TLS/NPTL support is enabled

base/glibc/glibc.conf

@@ -78,6 +78,13 @@ if [ $SDECFG_PKG_GLIBC_TLS = 1 ]; then
 		var_append configcache ' ' "libc_cv_forced_unwind=yes"
 		var_append configcache ' ' "libc_cv_c_cleanup=yes"
 	fi
+
+	# help building/installing correct glibc headers at toolchain stage
+	if atstage toolchain; then
+		case "$arch" in
+			x86) var_append configcache ' ' "libc_cv_386_tls=yes" ;;
+		esac
+	fi
 else
 	var_append glibc_addons "," "linuxthreads"
 	var_append extraconfopt " " "--without-__thread"