Fixup measurement for --trace-compile-timing w/ nested compilations. (#59363)

Use a separate inference_start and compilation_start, where
compilation_start does not do anything special for reentrancy.

Here is an example which has a quick-to-compile nested dynamic dispatch,
but that nested function runs for a long time:
```julia
./julia --startup=no --trace-compile=stderr --trace-compile-timing -e '
  Base.@assume_effects :foldable function nested1(x)
      sum(collect(x for _ in 1:1000_000_000))
  end
  f1(x) = nested1(sizeof(x)) + x
  f1(2)'
#=   12.7 ms =# precompile(Tuple{typeof(Main.nested1), Int64})
#= 3809.3 ms =# precompile(Tuple{typeof(Main.f1), Int64})
```
This fixes a small issue introduced here:
https://github.com/JuliaLang/julia/pull/59220/files#r2292021838

(cherry picked from commit be59100)

Author: NHDaly

src/gf.c

@@ -3483,7 +3483,8 @@ jl_code_instance_t *jl_compile_method_internal(jl_method_instance_t *mi, size_t
     // Ok, compilation is enabled. We'll need to try to compile something (probably).
 
     // Everything from here on is considered (user facing) compile time
-    uint64_t start = jl_typeinf_timing_begin();
+    uint64_t compilation_start = jl_hrtime();
+    uint64_t inference_start = jl_typeinf_timing_begin(); // Special-handling for reentrancy
 
     // Is a recompile if there is cached code, and it was compiled (not only inferred) before
     int is_recompile = 0;
@@ -3510,14 +3511,14 @@ jl_code_instance_t *jl_compile_method_internal(jl_method_instance_t *mi, size_t
 
     if (codeinst) {
         if (jl_is_compiled_codeinst(codeinst)) {
-            jl_typeinf_timing_end(start, is_recompile);
+            jl_typeinf_timing_end(inference_start, is_recompile);
             // Already compiled - e.g. constabi, or compiled by a different thread while we were waiting.
             return codeinst;
         }
 
         JL_GC_PUSH1(&codeinst);
         int did_compile = jl_compile_codeinst(codeinst);
-        double compile_time = jl_hrtime() - start;
+        double compile_time = jl_hrtime() - compilation_start;
 
         if (jl_atomic_load_relaxed(&codeinst->invoke) == NULL) {
             // Something went wrong. Bail to the fallback path.
@@ -3547,7 +3548,7 @@ jl_code_instance_t *jl_compile_method_internal(jl_method_instance_t *mi, size_t
         if (ucache_invoke != jl_fptr_sparam &&
             ucache_invoke != jl_fptr_interpret_call) {
             // only these care about the exact specTypes, otherwise we can use it directly
-            jl_typeinf_timing_end(start, is_recompile);
+            jl_typeinf_timing_end(inference_start, is_recompile);
             return ucache;
         }
         uint8_t specsigflags;
@@ -3565,7 +3566,7 @@ jl_code_instance_t *jl_compile_method_internal(jl_method_instance_t *mi, size_t
         jl_mi_cache_insert(mi, codeinst);
     }
     jl_atomic_store_relaxed(&codeinst->precompile, 1);
-    jl_typeinf_timing_end(start, is_recompile);
+    jl_typeinf_timing_end(inference_start, is_recompile);
     return codeinst;
 }