Fix some paging related bugs exposed by the spawn stress test.

- Process::exec() needs to restore the original paging scope when called
  on a non-current process.
- Add missing InterruptDisabler guards around g_processes access.
- Only flush the TLB when modifying the active page tables.

AK/printf.cpp

@@ -1,5 +1,3 @@
-#define ALWAYS_INLINE inline __attribute__ ((always_inline))
-
 typedef unsigned char byte;
 typedef unsigned short word;
 typedef unsigned int dword;