Kernel+LibELF: Support initializing values of TLS data

Previously, TLS data was always zero-initialized.

To support initializing the values of TLS data, sys$allocate_tls now
receives a buffer with the desired initial data, and copies it to the
master TLS region of the process.

The DynamicLinker gathers the initial TLS image and passes it to
sys$allocate_tls.

We also now require the size passed to sys$allocate_tls to be
page-aligned, to make things easier. Note that this doesn't waste memory
as the TLS data has to be allocated in separate pages anyway.

Userland/Libraries/LibC/mman.cpp

@@ -73,9 +73,9 @@ int madvise(void* address, size_t size, int advice)
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }
 
-void* allocate_tls(size_t size)
+void* allocate_tls(const char* initial_data, size_t size)
 {
-    ptrdiff_t rc = syscall(SC_allocate_tls, size);
+    ptrdiff_t rc = syscall(SC_allocate_tls, initial_data, size);
     if (rc < 0 && -rc < EMAXERRNO) {
         errno = -rc;
         return MAP_FAILED;

Userland/Libraries/LibC/mman.h

@@ -40,6 +40,6 @@ int munmap(void*, size_t);
 int mprotect(void*, size_t, int prot);
 int set_mmap_name(void*, size_t, const char*);
 int madvise(void*, size_t, int advice);
-void* allocate_tls(size_t);
+void* allocate_tls(const char* initial_data, size_t);
 
 __END_DECLS