elfconvert: Pin the underlying thread_local crate version

This is a temporary fix until we clean up the nightly toolchain
dependency.

Change-Id: Iff643a26b16a8e764eb6b267ad2a854fda6e5662

misc/elfconvert/Cargo.toml

diff --git a/misc/elfconvert/Cargo.toml b/misc/elfconvert/Cargo.toml
index 1e7d26d..37899c7 100644
--- a/misc/elfconvert/Cargo.toml
+++ b/misc/elfconvert/Cargo.toml
@@ -18,6 +18,10 @@
 edition = "2018"
 
 [dependencies]
+# TODO(sleffler): Remove thread_local version pin from the underlying dependency
+# when we clean up the nightly toolchain.
+thread_local = "=1.1.4"
+
 clap = { version = "3.2", features = [ "derive" ] }
 log = { version = "0.4" }
 stderrlog = { version = "0.5" }