Fix pyflame for code compiled with ld -z separate-code

[randomstuff]

This generates VAS layouts like this:

555555554000-5555555a8000 r--p 00000000 08:02 919707                     /opt/python-3.6.8/bin/python3.6
5555555a8000-55555573d000 r-xp 00054000 08:02 919707                     /opt/python-3.6.8/bin/python3.6
55555573d000-5555557ce000 r--p 001e9000 08:02 919707                     /opt/python-3.6.8/bin/python3.6
5555557cf000-555555835000 rw-p 0027a000 08:02 919707                     /opt/python-3.6.8/bin/python3.6
555555835000-555555865000 rw-p 00000000 00:00 0                          [heap]
7ffff7fd0000-7ffff7fd3000 r--p 00000000 00:00 0                          [vvar]
7ffff7fd3000-7ffff7fd5000 r-xp 00000000 00:00 0                          [vdso]
7ffff7fd5000-7ffff7fd6000 r--p 00000000 08:02 265255                     /lib/x86_64-linux-gnu/ld-2.28.so
7ffff7fd6000-7ffff7ff4000 r-xp 00001000 08:02 265255                     /lib/x86_64-linux-gnu/ld-2.28.so
7ffff7ff4000-7ffff7ffc000 r--p 0001f000 08:02 265255                     /lib/x86_64-linux-gnu/ld-2.28.so
7ffff7ffc000-7ffff7ffe000 rw-p 00026000 08:02 265255                     /lib/x86_64-linux-gnu/ld-2.28.so
7ffff7ffe000-7ffff7fff000 rw-p 00000000 00:00 0
7ffffffde000-7ffffffff000 rw-p 00000000 00:00 0                          [stack]

This is enabled by default on Linux/x86 since 2.29 (f6aec96dce1ddbd8961a3aa8a2925db2021719bb).

[CLAassistant]

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[randomstuff]

This fixes pyflame on 3.6 (including 3.6.6+) for me. It won't work for 3.7 because there is no _PyThreadState_Current symbol anymore.

#  define _PyThreadState_Current _PyRuntime.gilstate.tstate_current 

I'll try to have a look at that later on.

[randomstuff]

This should fix #165 / #157.

[gaetano-guerriero]

This makes pyflame usable again for me with python 2.7.16 (debian buster), will this be merged ?