Fix segfaults related to sanitizers+jemalloc

It looks to be the case that Rust's standard allocator, jemalloc, is
incompatible with sanitizers. The incompatibility, for whatever reason,
seems to cause segfaults at runtime when jemalloc is linked with
sanitizers.

Without actually trying to figure out what's going on here this commit
instead takes the hammer of "let's remove jemalloc when testing". The
`tor_allocate` crate now by default switches to the system allocator
(eventually this will want to be the tor allocator). Most crates then
link to `tor_allocate` ot pick this up, but the `smartlist` crate had to
manually switch to the system allocator in testing and the `external`
crate had to be sure to link to `tor_allocate`.

The final gotcha here is that this patch also switches to
unconditionally passing `--target` to Cargo. For weird and arcane
reasons passing `--target` with the host target of the compiler (which
Cargo otherwise uses as the default) is different than not passing
`--target` at all. This ensure that our custom `RUSTFLAGS` with
sanitizer options doesn't make its way into build scripts, just the
final testing artifacts.

2 files changed, 3 insertions, 4 deletions

diff --git a/src/rust/external/Cargo.toml b/src/rust/external/Cargo.toml
index 4735144ee6..d5c3a739e0 100644
--- a/src/rust/external/Cargo.toml
+++ b/src/rust/external/Cargo.toml
@@ -5,9 +5,8 @@ name = "external"
 
 [dependencies]
 libc = "=0.2.39"
-
-[dependencies.smartlist]
-path = "../smartlist"
+smartlist = { path = "../smartlist" }
+tor_allocate = { path = "../tor_allocate" }
 
 [lib]
 name = "external"
diff --git a/src/rust/external/lib.rs b/src/rust/external/lib.rs
index b72a4f6e4c..d68036fcad 100644
--- a/src/rust/external/lib.rs
+++ b/src/rust/external/lib.rs
@@ -8,7 +8,7 @@
 //! module implementing this functionality repeatedly.
 
 extern crate libc;
-
+extern crate tor_allocate;
 extern crate smartlist;
 
 pub mod crypto_digest;