perf build failure with newer glibc headers

[Laura Abbott <labbott@redhat.com>]

Hi,

While doing some build experiments, I found a compile failure with perf and jvmti:

BUILDSTDERR:   gcc -Wp,-MD,./.xsk.o.d -Wp,-MT,xsk.o -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-gcc-jvmti/jvmti_agent.c:48:21: error: static declaration of 'gettid' follows non-static declaration
BUILDSTDERR:    48 | static inline pid_t gettid(void)
BUILDSTDERR:       |                     ^~~~~~
BUILDSTDERR: In file included from /usr/include/unistd.h:1170,
BUILDSTDERR:                  from jvmti/jvmti_agent.c:33:
BUILDSTDERR: /usr/include/bits/unistd_ext.h:40:16: note: previous declaration of 'gettid' was here
BUILDSTDERR:    40 | extern __pid_t gettid (void) __THROW;
BUILDSTDERR:       |                ^~~~~~


This is with the newer glibc headers that came into Fedora earlier this week
(glibc-2.29.9000-27.fc31)  It looks like the newer headers now define gettid
so the in file gettid no longer works. Note this was a custom build with
jvmti enabled as regular Fedora doesn't have it enabled which is why this
wasn't reported elsewhere.

I don't know enough about either the glibc headers or perf to make a suggestion
on how to fix this but I'm happy to test.

Thanks,
Laura