[roll] Roll llvm-project/libc [libc] clean up printf error codes

Move the constants for printf's return values into core_structs, and
update the converters to match.

Reviewed By: lntue

Differential Revision: https://reviews.llvm.org/D128767

GitOrigin-RevId: cb3afdab11b79153d89592d2c79c12939c4526b5
Original-Revision: 78f1b2aed278d56391f91fef455de0a3926a4b58
Change-Id: Iafce358d6428213f0e5a30d07a3c758a810b7319

third_party/flower

diff --git a/third_party/flower b/third_party/flower
index 5e9e04a..8e42699 100644
--- a/third_party/flower
+++ b/third_party/flower
@@ -254,7 +254,7 @@
     <project name="llvm-project/libc"
              path="third_party/llvm-libc/src"
              remote="https://llvm.googlesource.com/llvm-project/libc"
-             revision="67363eed9f65ccfd1341b4e624dcb752d864691c"/>
+             revision="78f1b2aed278d56391f91fef455de0a3926a4b58"/>
     <project name="third_party/lz4"
              path="third_party/lz4"
              remote="https://fuchsia.googlesource.com/third_party/lz4"