fix parsing of env

Author: vchuravy

src/threading.c

@@ -659,7 +659,11 @@ void jl_init_threading(void)
     jl_n_sweepthreads = jl_options.nsweepthreads;
     if (jl_n_markthreads == -1) { // --gcthreads not specified
         if ((cp = getenv(NUM_GC_THREADS_NAME))) { // ENV[NUM_GC_THREADS_NAME] specified
-            jl_n_markthreads = (uint64_t)strtol(cp, NULL, 10) - 1;
+            errno = 0;
+            jl_n_markthreads = (uint64_t)strtol(cp, &endptr, 10) - 1;
+            if (errno != 0 || endptr == cp || nthreads <= 0)
+                jl_n_markthreads = 0;
+            cp = endptr;
             if (*cp == ',') {
                 cp++;
                 errno = 0;

test/cmdlineargs.jl

@@ -372,7 +372,7 @@ let exename = `$(Base.julia_cmd()) --startup-file=no --color=no`
     end
 
     withenv("JULIA_NUM_GC_THREADS" => "2,1") do
-        @test_broken read(`$exename -e $code`, String) == "3"
+        @test read(`$exename -e $code`, String) == "3"
     end
 
     # --machine-file