Tidy up gdb_c_test.

1) Make gdb_c_test.rs more lean by removing command line arguments
that simply set env vars. We can just set the vars directly, e.g.:

YKD_LOG_IR=aot bin/gdb_c_test simple.c

It's a bit more typing, but it means this tool is smaller and more
resilient to env var additions/removals/changes. I note it still
referenced the old YKD_LOG_JITSTATE var, which was renamed to YK_LOG.

2) Remove no longer working -b.

The JIT code generator broke this, but I haven't missed it to be honest.

docs/src/dev/debugging.md

@@ -31,19 +31,7 @@ This will automatically compile and run the `tests/c/simple.c` test under GDB.
 This would be ideal if you have a crashing trace, as it will dump you into a
 GDB shell at the time of the crash.
 
-The tool has some other switches which are useful for other situations, e.g.:
-
-```
-bin/gdb_c_test -j -s -b10 simple.c
-```
-
-compiles and runs `tests/c/simple.c` test under GDB with [JIT state
-debugging](runtime_config.md#ykd_print_jitstate)
-enabled, with [compilation
-serialised](runtime_config.md#ykd_serialise_compilation), setting a
-breakpoint on the first 10 traces compiled.
-
-For a list of all switches available, run:
+To see what else you can do with `gdb_c_test`, run:
 
 ```
 bin/gdb_c_test --help

tests/src/bin/gdb_c_test.rs

@@ -13,22 +13,6 @@ struct Args {
     /// The test to attach gdb to.
     test_file: PathBuf,
 
-    /// Run the test with `YKD_LOG_IR` set to the specified value.
-    #[arg(short, long)]
-    log_ir: Option<String>,
-
-    /// Run the test with `YKD_LOG_JITSTATE=-`
-    #[arg(short = 'j', long)]
-    log_jitstate: bool,
-
-    /// Run the test with `YKD_SERIALISE_COMPILATION=1`
-    #[arg(short, long)]
-    serialise_compilation: bool,
-
-    /// Set breakpoints at the first `N` compiled traces.
-    #[arg(short = 'b', long)]
-    num_breaks: Option<usize>,
-
     /// Don't immediately run the program.
     #[arg(short = 'n', long)]
     wait_at_prompt: bool,
@@ -76,25 +60,6 @@ fn main() {
     let mut gdb = Command::new("gdb");
     gdb.arg(&binpath);
 
-    if args.serialise_compilation {
-        gdb.env("YKD_SERIALISE_COMPILATION", "1");
-    }
-
-    if args.log_jitstate {
-        gdb.env("YKD_LOG_JITSTATE", "1");
-    }
-
-    if let Some(irs) = args.log_ir {
-        gdb.env("YKD_LOG_IR", irs);
-    }
-
-    if let Some(num_breaks) = args.num_breaks {
-        gdb.args(["-ex", "set breakpoint pending on"]); // don't prompt for pending breaks.
-        for i in 0..num_breaks {
-            gdb.args(["-ex", &format!("b __yk_compiled_trace_{i}")]);
-        }
-    }
-
     if !args.wait_at_prompt {
         gdb.args(["-ex", "run"]);
     }