Save registers for conservative scanning (#159)

Adding context field to `mmtk__jl_tls_states_t` to reflect the changes
in mmtk/julia#61.

Author: udesou

julia/mmtk_julia_types.h

@@ -4,6 +4,7 @@
 #include <setjmp.h>	
 #include <stdint.h>
 #include <pthread.h>
+#include <ucontext.h>
 #include "mmtkMutator.h"
 
 typedef __SIZE_TYPE__ size_t;
@@ -438,6 +439,8 @@ typedef struct mmtk__jl_tls_states_t {
     MMTkMutatorContext mmtk_mutator;
     size_t malloc_sz_since_last_poll;
 
+    ucontext_t ctx_at_the_time_gc_started;
+
     // JULIA_DEBUG_SLEEPWAKE(
     //     uint64_t uv_run_enter;
     //     uint64_t uv_run_leave;

mmtk/Cargo.toml

@@ -10,7 +10,7 @@ edition = "2018"
 [package.metadata.julia]
 # Our CI matches the following line and extract mmtk/julia. If this line is updated, please check ci yaml files and make sure it works.
 julia_repo = "https://github.com/mmtk/julia.git"
-julia_version = "084d8a08f0cfc2b1d7acae2e000c165e8b11de5b"
+julia_version = "045bf87050653aa4ae996d3cdc052b1f3fcad7e6"
 
 [lib]
 crate-type = ["cdylib"]