Add strerrordesc_np() and strerrorname_np().

strerrordesc_np() isn't very useful (being just another name for
strerror()), but strerrorname_np() lets you get "ENOSYS" for ENOSYS,
which will make some of our test assertion messages clearer when we
switch over from strerror().

This also adds `%#m` formatting to all the relevant functions.

Test: treehugger
Change-Id: Icfe07a39a307d591c3f4f2a09d008dc021643062
diff --git a/libc/libc.map.txt b/libc/libc.map.txt
index e6ea3c2..824682b 100644
--- a/libc/libc.map.txt
+++ b/libc/libc.map.txt
@@ -1593,6 +1593,7 @@
     mktime_z;
     __riscv_flush_icache; # riscv64
     __riscv_hwprobe; # riscv64
+    strerrorname_np;
     tcgetwinsize;
     tcsetwinsize;
     timespec_getres;