oneAPI: make in-process NEO discovery real, fix LD_LIBRARY_PATH comment

Setting ENV["LD_LIBRARY_PATH"] inside __init__ cannot affect the running
process's dlopen search paths: glibc captures LD_LIBRARY_PATH once at process
startup, so the stated purpose (letting libsycl's bundled ze_lib find NEO's
libze_intel_gpu in-process) was never served for the current process — only for
child processes that inherit the environment.

dlopen the NEO driver by full path in __init__ so it is resident before libsycl
loads; a later dlopen("libze_intel_gpu.so.1") by libsycl's bundled loader then
resolves to it by soname without a path search. Keep extending LD_LIBRARY_PATH
but correct the comment to say it only covers spawned worker processes. Verified
oneMKL (which loads libsycl and needs NEO discovery) still works.

Addresses PR_REVIEW.md finding #10.

Author: michel2323

src/oneAPI.jl

@@ -17,6 +17,8 @@ using LLVM
 using LLVM.Interop
 using Core: LLVMPtr
 
+import Libdl
+
 # Load both SPIR-V codegen back-ends: GPUCompiler resolves the tool from the target's
 # `backend` field (`:khronos` -> translator, `:llvm` -> LLVM back-end) via a LazyModule that
 # looks the JLL up in `Base.loaded_modules`, so both must be loaded for either path to work.
@@ -144,9 +146,20 @@ function __init__()
                 # ensure that the OpenCL loader finds the ICD files from our artifacts
                 ENV["OCL_ICD_FILENAMES"] = oneL0.NEO_jll.libigdrcl
 
-                # ensure that libsycl's bundled ze_lib finds NEO's libze_intel_gpu via
-                # path-based driver discovery (it does not reuse the JLL-loaded module).
-                # Required when no system NEO is installed.
+                # libsycl (loaded later for oneMKL) carries its own bundled Level Zero loader
+                # that rediscovers the NEO driver by dlopen'ing it by soname rather than
+                # reusing our JLL-loaded module. dlopen NEO here by full path so it is already
+                # resident in this process before libsycl loads: a later
+                # dlopen("libze_intel_gpu.so.1") then resolves to this module by soname without
+                # needing a search path. Required when no system NEO is installed.
+                Libdl.dlopen(oneL0.NEO_jll.libze_intel_gpu; throw_error = false)
+
+                # Extend LD_LIBRARY_PATH with the NEO directory as well. NOTE: this does NOT
+                # affect the running process's own dlopen search — glibc captures
+                # LD_LIBRARY_PATH once at startup — so it serves only *child* processes (e.g.
+                # the multi-worker test suite) that inherit the environment and do their own
+                # path-based driver discovery. In-process discovery is handled by the dlopen
+                # above (and by ZE_ENABLE_ALT_DRIVERS, set in oneL0's __init__).
                 neo_libdir = dirname(oneL0.NEO_jll.libze_intel_gpu)
                 ld = get(ENV, "LD_LIBRARY_PATH", "")
                 if !occursin(neo_libdir, ld)