Update backtrace from 0.3.75 to 0.3.76

Summary:
Using a git dependency a few commits after 0.3.76 in order to pull in rust-lang/backtrace-rs#744, which fixes a build error on Windows when using `cfg(windows_raw_dylib)`.

```lang=log,counterexample
error[E0308]: mismatched types
   --> third-party\rust\vendor\backtrace-0.3.76\src\dbghelp.rs:87:76
    |
 35 | / macro_rules! dbghelp {
 36 | |     (extern "system" {
 37 | |         $(fn $name:ident($($arg:ident: $argty:ty),*) -> $ret: ty;)*
 38 | |     }) => (
...   |
 87 | |                         let _: unsafe extern "C" fn($($argty),*) -> $ret = super::windows_sys::$name;
    | |                                -----------------------------------------   ^^^^^^^^^^^^^^^^^^^^^^^^^ expected "C" fn, found "system" fn
    | |                                |
    | |                                expected due to this
...   |
126 | | }
    | |_- in this expansion of `dbghelp!`
127 |
128 | / dbghelp! {
129 | |     extern "system" {
130 | |         fn SymGetOptions() -> u32;
131 | |         fn SymSetOptions(options: u32) -> u32;
...   |
223 | | }
    | |_- in this macro invocation
    |
    = note: expected fn pointer `unsafe extern "C" fn(_, _) -> _`
                  found fn item `unsafe extern "system" fn(_, _) -> _ {windows_sys::SymAddrIncludeInlineTrace}`
```

Difference from 0.3.76:
rust-lang/backtrace-rs@backtrace-v0.3.76...df979dc

Context: https://fb.workplace.com/groups/learningrust/posts/4270473293223523

Reviewed By: cjlongoria

Differential Revision: D91645033

fbshipit-source-id: 5c7131a86b89090e9d72f2aa82b5d918065d029b

Author: David Tolnay

eden/fs/Cargo.toml

@@ -1,6 +1,7 @@
 [patch.crates-io]
 abomonation = { git = "https://github.com/markbt/abomonation", rev = "0f43346d2afa2aedc64d61f3f4273e8d1e454642" }
 audio_streams = { git = "https://github.com/google/crosvm", rev = "7d2e877a2a0a772c199fe8b6b51aec7c1b166467" }
+backtrace = { git = "https://github.com/rust-lang/backtrace-rs", rev = "df979dcf80027eb047d7bb9e0874710c15009f31" }
 base64urlsafedata = { git = "https://github.com/kanidm/webauthn-rs.git", rev = "d278c56adfa39a0723c79bdcd461644194bc5138" }
 bindgen = { git = "https://github.com/jsgf/rust-bindgen", rev = "4d385d21c160e6ee1f443aeb7e00528a1dc7fd44" }
 bindgen-cli = { git = "https://github.com/jsgf/rust-bindgen", rev = "4d385d21c160e6ee1f443aeb7e00528a1dc7fd44" }

eden/mononoke/Cargo.toml

@@ -1,6 +1,7 @@
 [patch.crates-io]
 abomonation = { git = "https://github.com/markbt/abomonation", rev = "0f43346d2afa2aedc64d61f3f4273e8d1e454642" }
 audio_streams = { git = "https://github.com/google/crosvm", rev = "7d2e877a2a0a772c199fe8b6b51aec7c1b166467" }
+backtrace = { git = "https://github.com/rust-lang/backtrace-rs", rev = "df979dcf80027eb047d7bb9e0874710c15009f31" }
 base64urlsafedata = { git = "https://github.com/kanidm/webauthn-rs.git", rev = "d278c56adfa39a0723c79bdcd461644194bc5138" }
 bindgen = { git = "https://github.com/jsgf/rust-bindgen", rev = "4d385d21c160e6ee1f443aeb7e00528a1dc7fd44" }
 bindgen-cli = { git = "https://github.com/jsgf/rust-bindgen", rev = "4d385d21c160e6ee1f443aeb7e00528a1dc7fd44" }