rename sys allocator's sys_alloc symbol to tcmalloc_sys_alloc

Since we're not building with hidden visibility, symbols of other DSOs
can interpose our symbols. And sys_alloc is just too generic name.

And in fact erlang runtime has sys_alloc function. Which means we're
trying to write to it's first bytes as part of initializing system
allocator and crash.

This should fix issue gperftools#843.

src/system-alloc.cc

@@ -122,7 +122,7 @@ static size_t pagesize = 0;
 #endif
 
 // The current system allocator
-SysAllocator* sys_alloc = NULL;
+SysAllocator* tcmalloc_sys_alloc = NULL;
 
 // Number of bytes taken from system.
 size_t TCMalloc_SystemTaken = 0;
@@ -484,7 +484,7 @@ void InitSystemAllocators(void) {
     sdef->SetChildAllocator(mmap, 1, mmap_name);
   }
 
-  sys_alloc = tc_get_sysalloc_override(sdef);
+  tcmalloc_sys_alloc = tc_get_sysalloc_override(sdef);
 }
 
 void* TCMalloc_SystemAlloc(size_t size, size_t *actual_size,
@@ -507,7 +507,7 @@ void* TCMalloc_SystemAlloc(size_t size, size_t *actual_size,
     actual_size = &actual_size_storage;
   }
 
-  void* result = sys_alloc->Alloc(size, actual_size, alignment);
+  void* result = tcmalloc_sys_alloc->Alloc(size, actual_size, alignment);
   if (result != NULL) {
     CHECK_CONDITION(
       CheckAddressBits<kAddressBits>(

src/system-alloc.h

@@ -84,7 +84,7 @@ extern PERFTOOLS_DLL_DECL
 void TCMalloc_SystemCommit(void* start, size_t length);
 
 // The current system allocator.
-extern PERFTOOLS_DLL_DECL SysAllocator* sys_alloc;
+extern PERFTOOLS_DLL_DECL SysAllocator* tcmalloc_sys_alloc;
 
 // Number of bytes taken from system.
 extern PERFTOOLS_DLL_DECL size_t TCMalloc_SystemTaken;

src/tcmalloc.cc

@@ -750,12 +750,12 @@ class TCMallocImplementation : public MallocExtension {
 
   virtual SysAllocator* GetSystemAllocator() {
     SpinLockHolder h(Static::pageheap_lock());
-    return sys_alloc;
+    return tcmalloc_sys_alloc;
   }
 
   virtual void SetSystemAllocator(SysAllocator* alloc) {
     SpinLockHolder h(Static::pageheap_lock());
-    sys_alloc = alloc;
+    tcmalloc_sys_alloc = alloc;
   }
 
   virtual void ReleaseToSystem(size_t num_bytes) {

src/windows/system-alloc.cc

@@ -46,7 +46,7 @@
 static SpinLock spinlock(SpinLock::LINKER_INITIALIZED);
 
 // The current system allocator declaration
-SysAllocator* sys_alloc = NULL;
+SysAllocator* tcmalloc_sys_alloc = NULL;
 // Number of bytes taken from system.
 size_t TCMalloc_SystemTaken = 0;
 
@@ -121,7 +121,7 @@ SysAllocator* tc_get_sysalloc_override(SysAllocator *def)
 static bool system_alloc_inited = false;
 void InitSystemAllocators(void) {
   VirtualSysAllocator *alloc = new (virtual_space) VirtualSysAllocator();
-  sys_alloc = tc_get_sysalloc_override(alloc);
+  tcmalloc_sys_alloc = tc_get_sysalloc_override(alloc);
 }
 
 extern PERFTOOLS_DLL_DECL
@@ -134,7 +134,7 @@ void* TCMalloc_SystemAlloc(size_t size, size_t *actual_size,
     system_alloc_inited = true;
   }
 
-  void* result = sys_alloc->Alloc(size, actual_size, alignment);
+  void* result = tcmalloc_sys_alloc->Alloc(size, actual_size, alignment);
   if (result != NULL) {
     if (actual_size) {
       TCMalloc_SystemTaken += *actual_size;