gdb: fix Add python3 linkage support

[ttimasdf]

• Have you followed the guidelines for contributing?
• Have you checked that there aren't other open pull requests for the same formula update/change?
• Have you built your formula locally with brew install --build-from-source <formula>, where <formula> is the name of the formula you're submitting?
• Does your build pass brew audit --strict <formula> (after doing brew install <formula>)?

---

Description:
I've made a patch to configure process and make it possible to compile gdb against python3. When launched with python3, gdb/python/python-config.py in the source file generates some flags that clang may not recognize. I tried to patch it but with no luck. So instead I choose the python3-config that comes with python, it works.

The difference of their output:

$ python3 python/python-config.py --ldflags
-L/usr/local/opt/python3/Frameworks/Python.framework/Versions/3.6/lib/python3.6/config-3.6m-darwin -ldl -framework CoreFoundation -lpython3.6m -Wl,-stack_size,1000000 -framework CoreFoundation Python.framework/Versions/3.6/Python

$ python3-config --ldflags
-L/usr/local/opt/python3/Frameworks/Python.framework/Versions/3.6/lib/python3.6/config-3.6m-darwin -lpython3.6m -ldl -framework CoreFoundation

[ilovezfs]

Not sure I understand this.

iMac-TMP:~ joe$ gdb
GNU gdb (GDB) 8.0.1
Copyright (C) 2017 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-apple-darwin15.6.0".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word".
(gdb) 

[ttimasdf]

@ilovezfs sorry I was a bit lazy writing a description. now updated. After applied the patch in the commit, we could choose to build gdb with python3, just another option ;-p

[ilovezfs]

@ttimasdf Thanks for explaining ❤️. We'll need to get the patch reported and accepted upstream before we can ship this, I'm afraid.

[ttimasdf]

Debian/Ubuntu guys have already had a patch years ago at version 7.8-0ubuntu2 and 7.6.2-1.1(jessie) But it has never been accepted by upstream, regarding the maybe-broken python-config on other platforms. Maybe we should add the patch by our own as well.

[ttimasdf]

another fix that should work, inspired from original python3.6-config

diff --git a/gdb/python/python-config.py.origin b/gdb/python/python-config.py
index c2b2969..554dac9 100644
--- a/gdb/python/python-config.py.origin
+++ b/gdb/python/python-config.py
@@ -72,7 +72,7 @@ for opt in opt_flags:
                     libs.insert(0, '-L' + getvar('LIBPL'))
                 elif os.name == 'nt':
                     libs.insert(0, '-L' + sysconfig.PREFIX + '/libs')
-            if getvar('LINKFORSHARED') is not None:
+            if not getvar('PYTHONFRAMEWORK'):
                 libs.extend(getvar('LINKFORSHARED').split())
         print (to_unix_path(' '.join(libs)))

Any suggestions?

[ilovezfs]

@BrewTestBot test this please

[ilovezfs]

@BrewTestBot test this please

[ilovezfs]

We'll need this patch upstreamed before it can be accepted in Homebrew. Sorry @ttimasdf and thanks for the PR nonetheless!