Kernel+LibC+LibELF: Set stack size based on PT_GNU_STACK during execve

Some programs explicitly ask for a different initial stack size than
what the OS provides. This is implemented in ELF by having a
PT_GNU_STACK header which has its p_memsz set to the amount that the
program requires. This commit implements this policy by reading the
p_memsz of the header and setting the main thread stack size to that.
ELF::Image::validate_program_headers ensures that the size attribute is
a reasonable value.

Userland/Libraries/LibELF/Image.cpp

@@ -12,6 +12,7 @@
 #include <AK/QuickSort.h>
 #include <AK/StringBuilder.h>
 #include <AK/StringView.h>
+#include <Kernel/API/serenity_limits.h>
 #include <LibELF/Image.h>
 #include <LibELF/Validation.h>
 #include <limits.h>