cmd/compile: reenable inlstaticinit

This was disabled in CL 452676 out of an abundance of caution,
but further analysis has shown that the failures were not being
caused by this optimization. Instead the sequence of commits was:

CL 450136 cmd/compile: handle simple inlined calls in staticinit
...
CL 449937 archive/tar, archive/zip: return ErrInsecurePath for unsafe paths
...
CL 451555 cmd/compile: fix static init for inlined calls

The failures in question became compile failures in the first CL
and started building again after the last CL.
But in the interim the code had been broken by the middle CL.
CL 451555 was just the first time that the tests could run and fail.

For #30820.

Change-Id: I65064032355b56fdb43d9731be2f9f32ef6ee600
Reviewed-on: https://go-review.googlesource.com/c/go/+/452817
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Russ Cox <rsc@golang.org>
Auto-Submit: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/cmd/compile/internal/base/debug.go

@@ -31,7 +31,7 @@ type DebugFlags struct {
 	GCProg                int    `help:"print dump of GC programs"`
 	Gossahash             string `help:"hash value for use in debugging the compiler"`
 	InlFuncsWithClosures  int    `help:"allow functions with closures to be inlined" concurrent:"ok"`
-	InlStaticInit         int    `help:"allow static initialization of inlined calls"`
+	InlStaticInit         int    `help:"allow static initialization of inlined calls" concurrent:"ok"`
 	InterfaceCycles       int    `help:"allow anonymous interface cycles"`
 	Libfuzzer             int    `help:"enable coverage instrumentation for libfuzzer"`
 	LocationLists         int    `help:"print information about DWARF location list creation"`