force x86_64-v2 cpu for linux builds (fixup for #5674) (#5891)

actually force x86_64-v2 cpu
Forcing v3 postponed until build issues with rocksdb are resolved. 
Co-authored-by: Alex Pyattaev <alex.pyattaev@anza.xyz>

.cargo/config.toml

@@ -0,0 +1,3 @@
+[target.x86_64-unknown-linux-gnu]
+# When building for linux, target the minimal supported CPU
+rustflags = ["-Ctarget-cpu=x86-64-v2"]

Cargo.toml

@@ -1,6 +1,3 @@
-[build]
-rustflags = ["-Ctarget-cpu=x86-64-v3"]
-
 [profile.release-with-debug]
 inherits = "release"
 debug = true