gdbserver: Add PID parameter to linux_get_auxv and linux_get_hwcap

This patch doesn't change gdbserver behaviour, but after later changes are
made it avoids a null pointer dereference when HWCAP needs to be obtained
for a specific process while current_thread is nullptr.

Fixing linux_read_auxv, linux_get_hwcap and linux_get_hwcap2 to take a PID
parameter seems more correct than setting current_thread in one particular
code path.

Changes are propagated to allow passing the new parameter through the call
chain.

Approved-By: Simon Marchi <simon.marchi@efficios.com>

gdbserver/target.cc

@@ -346,8 +346,8 @@ process_stratum_target::supports_read_auxv ()
 }
 
 int
-process_stratum_target::read_auxv (CORE_ADDR offset, unsigned char *myaddr,
-				   unsigned int len)
+process_stratum_target::read_auxv (int pid, CORE_ADDR offset,
+				   unsigned char *myaddr, unsigned int len)
 {
   gdb_assert_not_reached ("target op read_auxv not supported");
 }