Use correct variable for threads auto (#44747)

--threads=auto uses jl_effective_threads to determine the number of threads to use,
so make sure the tests do too, otherwise this test will fail on our new cpu-restricted
runners.

Author: Keno

src/jl_exported_funcs.inc

@@ -103,6 +103,7 @@
     XX(jl_copy_ast) \
     XX(jl_copy_code_info) \
     XX(jl_cpu_threads) \
+    XX(jl_effective_threads) \
     XX(jl_crc32c_sw) \
     XX(jl_create_system_image) \
     XX(jl_cstr_to_string) \

src/julia.h

@@ -1635,6 +1635,7 @@ JL_DLLEXPORT int jl_errno(void) JL_NOTSAFEPOINT;
 JL_DLLEXPORT void jl_set_errno(int e) JL_NOTSAFEPOINT;
 JL_DLLEXPORT int32_t jl_stat(const char *path, char *statbuf) JL_NOTSAFEPOINT;
 JL_DLLEXPORT int jl_cpu_threads(void) JL_NOTSAFEPOINT;
+JL_DLLEXPORT int jl_effective_threads(void) JL_NOTSAFEPOINT;
 JL_DLLEXPORT long jl_getpagesize(void) JL_NOTSAFEPOINT;
 JL_DLLEXPORT long jl_getallocationgranularity(void) JL_NOTSAFEPOINT;
 JL_DLLEXPORT int jl_is_debugbuild(void) JL_NOTSAFEPOINT;

src/sys.c

@@ -436,7 +436,7 @@ JL_DLLEXPORT int jl_cpu_threads(void) JL_NOTSAFEPOINT
 #endif
 }
 
-int jl_effective_threads(void) JL_NOTSAFEPOINT
+JL_DLLEXPORT int jl_effective_threads(void) JL_NOTSAFEPOINT
 {
     int cpu = jl_cpu_threads();
     int masksize = uv_cpumask_size();

test/cmdlineargs.jl

@@ -218,7 +218,7 @@ let exename = `$(Base.julia_cmd()) --startup-file=no --color=no`
 
     # -t, --threads
     code = "print(Threads.nthreads())"
-    cpu_threads = ccall(:jl_cpu_threads, Int32, ())
+    cpu_threads = ccall(:jl_effective_threads, Int32, ())
     @test string(cpu_threads) ==
           read(`$exename --threads auto -e $code`, String) ==
           read(`$exename --threads=auto -e $code`, String) ==