[PATCH] gdb: fix IA64 build failure of linux-nat

[Sergei Trofimovich <slyfox@gentoo.org>]

From: Sergei Trofimovich <siarheit@google.com>

On IA64 built failed as:

```
ia64-linux-nat.c:352:29: error: 'gdbarch_num_regs' was not declared in this scope
  352 |   if (regno < 0 || regno >= gdbarch_num_regs (gdbarch))
      |                             ^~~~~~~~~~~~~~~~
```

The fix includes "gdbarch.h" header where symbol is declared.

	* gdb/ia64-linux-nat.c: include "gdbarch.h" to declare used
	'gdbarch_num_regs'.

Signed-off-by: Sergei Trofimovich <siarheit@google.com>
---
 gdb/ChangeLog        | 5 +++++
 gdb/ia64-linux-nat.c | 1 +
 2 files changed, 6 insertions(+)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index ac0beef5ad..0d921da325 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2020-05-19  Sergei Trofimovich  <siarheit@google.com>
+
+	* gdb/ia64-linux-nat.c: include "gdbarch.h" to declare used
+	'gdbarch_num_regs'.
+
 2020-05-19  Simon Marchi  <simon.marchi@efficios.com>
 
 	* dwarf2/read.c (quirk_rust_enum): Allocate enough fields.
diff --git a/gdb/ia64-linux-nat.c b/gdb/ia64-linux-nat.c
index 8f36ea78e7..b532e7a51c 100644
--- a/gdb/ia64-linux-nat.c
+++ b/gdb/ia64-linux-nat.c
@@ -21,6 +21,7 @@
 #include "defs.h"
 #include "inferior.h"
 #include "target.h"
+#include "gdbarch.h"
 #include "gdbcore.h"
 #include "regcache.h"
 #include "ia64-tdep.h"
-- 
2.26.2