[gdb/tdep] Support catch syscall pipe2 for i386

With test-case gdb.base/catch-syscall.exp and target board unix/-m32, we run
into:
...
(gdb) catch syscall pipe2^M
Unknown syscall name 'pipe2'.^M
(gdb) FAIL: gdb.base/catch-syscall.exp: determine pipe syscall: catch syscall pipe2
...

Fix this by:
- adding a pipe2 entry in gdb/syscalls/i386-linux.xml.in, and
- regenerating gdb/syscalls/i386-linux.xml using
  "xsltproc --output i386-linux.xml apply-defaults.xsl i386-linux.xml.in".

Tested on x86_64-linux with native and unix/-m32.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29056

---
 gdb/syscalls/i386-linux.xml    | 1 +
 gdb/syscalls/i386-linux.xml.in | 1 +
 2 files changed, 2 insertions(+)

diff --git a/gdb/syscalls/i386-linux.xml b/gdb/syscalls/i386-linux.xml
index a783dd10af3..4a7a2345186 100644
--- a/gdb/syscalls/i386-linux.xml
+++ b/gdb/syscalls/i386-linux.xml
@@ -334,4 +334,5 @@
   <syscall name="eventfd" number="323" groups="descriptor"/>
   <syscall name="fallocate" number="324" groups="descriptor"/>
   <syscall name="timerfd_settime" number="325" groups="descriptor"/>
+  <syscall name="pipe2" number="331" groups="descriptor"/>
 </syscalls_info>
diff --git a/gdb/syscalls/i386-linux.xml.in b/gdb/syscalls/i386-linux.xml.in
index e778ab54043..13c4d1d99d4 100644
--- a/gdb/syscalls/i386-linux.xml.in
+++ b/gdb/syscalls/i386-linux.xml.in
@@ -337,4 +337,5 @@
   <syscall name="eventfd" number="323"/>
   <syscall name="fallocate" number="324"/>
   <syscall name="timerfd_settime" number="325"/>
+  <syscall name="pipe2" number="331"/>
 </syscalls_info>