perf: squelch warnings from perl.h to compile-pass

Currently, a simple

  $ make

errors out because we compile with -Werror by default, turning all
warnings into errors.  Although no warnings are emitted by our code
itself, two kinds of warnings are emitted by perl.h (perl 5.18.0):

  -Wundef and -Wswitch-default

Use #pragma statements to squelch exactly those warnings, making perf
compile-pass.

Helped-by: Namhyung Kim <namhyung@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
perf/Perf-Trace-Util: regenerate Context.c

From Context.xs, using the procedure described in the README.

Cc: Tom Zanussi <tom.zanussi@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
perf/Perf-Trace-Util: add .gitignore

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>