commit 15d649f79d6b6dc336f6a32eec242b652a262a82
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Mar 25 18:24:37 2021

    libstdc++: Declare malloc for freestanding
    
    For a target with none of aligned_alloc, memalign etc. we defined our
    own aligned_alloc using malloc, so we need a declaration of malloc. As
    in libsupc++/new_op.cc we need to declare it ourselves for freestanding
    environments.
    
    libstdc++-v3/ChangeLog:
    
            * libsupc++/new_opa.cc [!_GLIBCXX_HOSTED]: Declare malloc.

diff --git a/libstdc++-v3/libsupc++/new_opa.cc b/libstdc++-v3/libsupc++/new_opa.cc
index 59296226e83..6b78729dc24 100644
--- a/libstdc++-v3/libsupc++/new_opa.cc
+++ b/libstdc++-v3/libsupc++/new_opa.cc
@@ -54,6 +54,10 @@ extern "C"
   void *posix_memalign(void **, size_t alignment, size_t size);
 # elif _GLIBCXX_HAVE_MEMALIGN
   void *memalign(size_t alignment, size_t size);
+# else
+  // A freestanding C runtime may not provide "malloc" -- but there is no
+  // other reasonable way to implement "operator new".
+  void *malloc(size_t);
 # endif
 }
 #endif