Move spinlock to a function static variable from global.

The current code hits static initializer check.
Moved to a function so that it will be initialized on demand.

Bug: 1119650
Test: Ran linux-rel tryjob.

Change-Id: Id77428a3754892c6f17fab48030d9f44673e37ac
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2364155Reviewed-by: Will Harris <wfh@chromium.org>
Commit-Queue: Hidehiko Abe <hidehiko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#800380}

third_party/tcmalloc/README.chromium

@@ -121,3 +121,4 @@ Modifications:
   compiler to optimize away a static constructor
 - Include <atomic> in malloc_extension.h due to std::atomic usage
 - Precompute the pointer mask for doubly linked free lists instead of computing it on each access.
+- Move spinlock to function static variable to fix static initializer check error.

third_party/tcmalloc/chromium/src/system-alloc.cc

@@ -248,8 +248,6 @@ void* AllocWithMmap(size_t length, bool is_aslr_enabled) {
 COMPILE_ASSERT(kAddressBits <= 8 * sizeof(void*),
                address_bits_larger_than_pointer_size);
 
-static SpinLock spinlock(SpinLock::LINKER_INITIALIZED);
-
 #if defined(HAVE_MMAP) || defined(MADV_FREE)
 #ifdef HAVE_GETPAGESIZE
 static size_t pagesize = 0;
@@ -638,6 +636,7 @@ void* TCMalloc_SystemAlloc(size_t size, size_t *actual_size,
   // Discard requests that overflow
   if (size + alignment < size) return NULL;
 
+  static SpinLock spinlock(SpinLock::LINKER_INITIALIZED);
   SpinLockHolder lock_holder(&spinlock);
 
   if (!system_alloc_inited) {