UserspaceEmulator+LibC: Use sys$emuctl() to disable auditing in malloc

It was fragile to use the address of the body of the memory management
functions to disable memory auditing within them. Functions called from
these did not get exempted from the audits, so in some cases
UserspaceEmulator reported bogus heap buffer overflows.

Memory auditing did not work at all on Clang because when querying the
addresses, their offset was taken relative to the base of `.text` which
is not the first segment in the `R/RX/RW(RELRO)/RW(non-RELRO)` layout
produced by LLD.

Similarly to when setting metadata about the allocations, we now use the
`emuctl` system call to selectively suppress auditing when we reach
these functions. This ensures that functions called from `malloc` are
affected too, and no issues occur because of the inconsistency between
Clang and GCC memory layouts.

Userland/Libraries/LibC/malloc.cpp

@@ -73,6 +73,19 @@ ALWAYS_INLINE static void ue_notify_chunk_size_changed(const void* block, size_t
         syscall(SC_emuctl, 4, chunk_size, (FlatPtr)block);
 }
 
+struct MemoryAuditingSuppressor {
+    ALWAYS_INLINE MemoryAuditingSuppressor()
+    {
+        if (s_in_userspace_emulator)
+            syscall(SC_emuctl, 7);
+    }
+    ALWAYS_INLINE ~MemoryAuditingSuppressor()
+    {
+        if (s_in_userspace_emulator)
+            syscall(SC_emuctl, 8);
+    }
+};
+
 struct MallocStats {
     size_t number_of_malloc_calls;
 
@@ -399,6 +412,7 @@ static void free_impl(void* ptr)
 
 [[gnu::flatten]] void* malloc(size_t size)
 {
+    MemoryAuditingSuppressor suppressor;
     void* ptr = malloc_impl(size, CallerWillInitializeMemory::No);
     if (s_profiling)
         perf_event(PERF_EVENT_MALLOC, size, reinterpret_cast<FlatPtr>(ptr));
@@ -407,6 +421,7 @@ static void free_impl(void* ptr)
 
 [[gnu::flatten]] void free(void* ptr)
 {
+    MemoryAuditingSuppressor suppressor;
     if (s_profiling)
         perf_event(PERF_EVENT_FREE, reinterpret_cast<FlatPtr>(ptr), 0);
     ue_notify_free(ptr);
@@ -415,6 +430,7 @@ static void free_impl(void* ptr)
 
 void* calloc(size_t count, size_t size)
 {
+    MemoryAuditingSuppressor suppressor;
     if (Checked<size_t>::multiplication_would_overflow(count, size)) {
         errno = ENOMEM;
         return nullptr;
@@ -428,6 +444,7 @@ void* calloc(size_t count, size_t size)
 
 size_t malloc_size(void* ptr)
 {
+    MemoryAuditingSuppressor suppressor;
     if (!ptr)
         return 0;
     void* page_base = (void*)((FlatPtr)ptr & ChunkedBlock::block_mask);
@@ -449,6 +466,7 @@ size_t malloc_good_size(size_t size)
 
 void* realloc(void* ptr, size_t size)
 {
+    MemoryAuditingSuppressor suppressor;
     if (!ptr)
         return malloc(size);
     if (!size) {