allocator: Fix __THROW and mallinfo for Musl

src/base/allocator/partition_allocator/src/partition_alloc/partition_root.cc

@@ -278,7 +278,12 @@ void PartitionAllocMallocInitOnce() {
     return;
   }
 
-#if BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_CHROMEOS)
+#if defined(__MUSL__)
+  // Musl calls malloc() in pthread_atfork(), resulting in a deadlock.
+  static_cast<void>(BeforeForkInParent);
+  static_cast<void>(AfterForkInParent);
+  static_cast<void>(AfterForkInChild);
+#elif BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_CHROMEOS)
   // When fork() is called, only the current thread continues to execute in the
   // child process. If the lock is held, but *not* by this thread when fork() is
   // called, we have a deadlock.

src/base/allocator/partition_allocator/src/partition_alloc/shim/allocator_shim_default_dispatch_to_partition_alloc.cc

@@ -641,7 +641,7 @@ SHIM_ALWAYS_EXPORT int mallopt(int cmd, int value) __THROW {
 
 #endif  // !BUILDFLAG(IS_APPLE) && !BUILDFLAG(IS_ANDROID)
 
-#if BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_CHROMEOS)
+#if BUILDFLAG(IS_LINUX) && !defined(__MUSL__) || BUILDFLAG(IS_CHROMEOS)
 SHIM_ALWAYS_EXPORT struct mallinfo mallinfo(void) __THROW {
   partition_alloc::SimplePartitionStatsDumper allocator_dumper;
   Allocator()->DumpStats("malloc", true, &allocator_dumper);

src/base/allocator/partition_allocator/src/partition_alloc/shim/allocator_shim_internals.h

@@ -9,7 +9,8 @@
 
 #if defined(__GNUC__)
 
-#if BUILDFLAG(IS_POSIX)
+// Musl does not provide sys/cdefs.h
+#if BUILDFLAG(IS_POSIX) && !defined(__MUSL__)
 #include <sys/cdefs.h>  // for __THROW
 #endif
 

src/base/allocator/partition_allocator/src/partition_alloc/shim/allocator_shim_override_libc_symbols.h

@@ -25,6 +25,12 @@
 
 #include "partition_alloc/shim/allocator_shim_internals.h"
 
+// Musl does not specify anything for malloc() etc.
+#if defined(__MUSL__)
+#undef __THROW
+#define __THROW
+#endif
+
 extern "C" {
 
 // WARNING: Whenever a new function is added there (which, surprisingly enough,