[libcxx][libcxxabi] Remove OVERRIDABLE_FUNCTION macro (#209323)

This is no longer needed, we can just use [[gnu::weak]] attribute.

GitOrigin-RevId: 6c6ecb376a940d16e17dae2d40dc076466898860

src/stdlib_new_delete.cpp

diff --git a/src/stdlib_new_delete.cpp b/src/stdlib_new_delete.cpp
index 164a263..9f53894 100644
--- a/src/stdlib_new_delete.cpp
+++ b/src/stdlib_new_delete.cpp
@@ -59,7 +59,7 @@
   return p;
 }
 
-OVERRIDABLE_FUNCTION void* operator new(std::size_t size) _THROW_BAD_ALLOC {
+[[gnu::weak]] void* operator new(std::size_t size) _THROW_BAD_ALLOC {
   void* p = operator_new_impl(size);
   if (p == nullptr)
     __throw_bad_alloc_shim();
@@ -90,7 +90,7 @@
 #endif
 }
 
-OVERRIDABLE_FUNCTION void* operator new[](size_t size) _THROW_BAD_ALLOC { return ::operator new(size); }
+[[gnu::weak]] void* operator new[](size_t size) _THROW_BAD_ALLOC { return ::operator new(size); }
 
 [[gnu::weak]] void* operator new[](size_t size, const std::nothrow_t&) noexcept {
 #if !_LIBCPP_HAS_EXCEPTIONS
@@ -150,7 +150,7 @@
   return p;
 }
 
-OVERRIDABLE_FUNCTION void* operator new(std::size_t size, std::align_val_t alignment) _THROW_BAD_ALLOC {
+[[gnu::weak]] void* operator new(std::size_t size, std::align_val_t alignment) _THROW_BAD_ALLOC {
   void* p = operator_new_aligned_impl(size, alignment);
   if (p == nullptr)
     __throw_bad_alloc_shim();
@@ -181,7 +181,7 @@
 #  endif
 }
 
-OVERRIDABLE_FUNCTION void* operator new[](size_t size, std::align_val_t alignment) _THROW_BAD_ALLOC {
+[[gnu::weak]] void* operator new[](size_t size, std::align_val_t alignment) _THROW_BAD_ALLOC {
   return ::operator new(size, alignment);
 }