set number of openblas threads to 1 while precompiling

Author: KristofferC

base/loading.jl

@@ -1684,12 +1684,14 @@ function create_expr_cache(pkg::PkgId, input::String, output::String, concrete_d
     deps_eltype = sprint(show, eltype(concrete_deps); context = :module=>nothing)
     deps = deps_eltype * "[" * join(deps_strs, ",") * "]"
     trace = isassigned(PRECOMPILE_TRACE_COMPILE) ? `--trace-compile=$(PRECOMPILE_TRACE_COMPILE[])` : ``
-    io = open(pipeline(`$(julia_cmd()::Cmd) -O0
-                       --output-ji $output --output-incremental=yes
-                       --startup-file=no --history-file=no --warn-overwrite=yes
-                       --color=$(have_color === nothing ? "auto" : have_color ? "yes" : "no")
-                       $trace
-                       -`, stderr = internal_stderr, stdout = internal_stdout),
+    io = open(pipeline(addenv(`$(julia_cmd()::Cmd) -O0
+                              --output-ji $output --output-incremental=yes
+                              --startup-file=no --history-file=no --warn-overwrite=yes
+                              --color=$(have_color === nothing ? "auto" : have_color ? "yes" : "no")
+                              $trace
+                              -`,
+                              "OPENBLAS_NUM_THREADS" => 1),
+                       stderr = internal_stderr, stdout = internal_stdout),
               "w", stdout)
     # write data over stdin to avoid the (unlikely) case of exceeding max command line size
     write(io.in, """