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.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