Fix few warnings

Remaining warnings (openlibm excluded):

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warning: src/c/dlmalloc.c:550:7: warning: mismatch in argument 3 type of built-in function ‘memcpy’; expected ‘long unsigned int’ [-Wbuiltin-declaration-mismatch]
warning:   550 | void *memcpy(void *dest, const void *src, size_t n);
warning:       |       ^~~~~~
warning: src/c/dlmalloc.c:551:7: warning: mismatch in argument 3 type of built-in function ‘memset’; expected ‘long unsigned int’ [-Wbuiltin-declaration-mismatch]
warning:   551 | void *memset(void *s, int c, size_t n);
warning:       |       ^~~~~~
warning: src/c/stdio.c:39:5: warning: mismatch in argument 2 type of built-in function ‘vsnprintf’; expected ‘long unsigned int’ [-Wbuiltin-declaration-mismatch]
warning:    39 | int vsnprintf(char * s, size_t n, const char * fmt, va_list ap);
warning:       |     ^~~~~~~~~
warning: src/c/stdio.c:41:5: warning: mismatch in argument 2 type of built-in function ‘snprintf’; expected ‘long unsigned int’ [-Wbuiltin-declaration-mismatch]
warning:    41 | int snprintf(char * s, size_t n, const char * fmt, ...) {
warning:       |     ^~~~~~~~
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pte_throw.c: In function ‘pte_throw’:
pte_throw.c:85:22: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
   85 |           exitCode = (unsigned) PTHREAD_CANCELED;
      |                      ^
pte_throw.c:88:22: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
   88 |           exitCode = (unsigned) sp->exitStatus;;
      |                      ^
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pthread_timechange_handler_np.c: In function ‘pthread_timechange_handler_np’:
pthread_timechange_handler_np.c:113:10: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
  113 |   return (void *) (result != 0 ? EAGAIN : 0);
      |          ^
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pte_threadStart.c: In function ‘pte_threadStart’:
pte_threadStart.c:245:10: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
  245 |   return (unsigned) status;
      |          ^
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warning: `extern` block uses type `core::panic::PanicInfo` which is not FFI-safe: this struct has unspecified layout
  --> src/crt0/src/lib.rs:35:29
   |
35 |         fn relibc_panic(pi: &::core::panic::PanicInfo) -> !;
   |                             ^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: #[warn(improper_ctypes)] on by default
   = help: consider adding a #[repr(C)] or #[repr(transparent)] attribute to this struct
###############################################################################
warning: `extern` block uses type `core::panic::PanicInfo` which is not FFI-safe: this struct has unspecified layout
  --> src/crti/src/lib.rs:55:29
   |
55 |         fn relibc_panic(pi: &::core::panic::PanicInfo) -> !;
   |                             ^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: #[warn(improper_ctypes)] on by default
   = help: consider adding a #[repr(C)] or #[repr(transparent)] attribute to this struct
###############################################################################
warning: `extern` block uses type `core::panic::PanicInfo` which is not FFI-safe: this struct has unspecified layout
  --> src/crtn/src/lib.rs:45:29
   |
45 |         fn relibc_panic(pi: &::core::panic::PanicInfo) -> !;
   |                             ^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: #[warn(improper_ctypes)] on by default
   = help: consider adding a #[repr(C)] or #[repr(transparent)] attribute to this struct
###############################################################################
warning: `extern` block uses type `core::panic::PanicInfo` which is not FFI-safe: this struct has unspecified layout
  --> src/ld_so/src/lib.rs:61:29
   |
61 |         fn relibc_panic(pi: &::core::panic::PanicInfo) -> !;
   |                             ^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: #[warn(improper_ctypes)] on by default
   = help: consider adding a #[repr(C)] or #[repr(transparent)] attribute to this struct
###############################################################################
unistd/brk.c: In function ‘main’:
unistd/brk.c:11:30: warning: pointer of type ‘void *’ used in arithmetic [-Wpointer-arith]
   11 |     int status = brk(current + 4096);
      |                              ^