[patch] Fix BZ 11420 -- configure uses incorrect link order when testing libpython

["Paul Pluzhnikov via gdb-patches" <gdb-patches@sourceware.org>]

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Greetings,

https://stackoverflow.com/a/49868387
https://sourceware.org/bugzilla/show_bug.cgi?id=11420

Configure uses "gcc -o conftest -g ... conftest.c -ldl -lncurses -lm -ldl
... -lpthread ... -lpython2.7" when deciding whether give libpython is
usable.

That of course is the wrong link order, and only works for shared libraries
(mostly by accident), and only on some systems.

Attached patch fixes this.

I am not sure about this part of the patch:

-  LIBS="$LIBS $new_LIBS"
+  LIBS="$new_LIBS $LIBS"

I think it's always better to prepend new libraries.

Thanks,

2018-04-17  Paul Pluzhnikov  <ppluzhnikov@google.com>

             PR gdb/11420
             * gdb/configure.ac: Prepend libpython.
             * gdb/python/python-config.py: Likewise.
             * gdb/configure: Regenerate.


-- 
Paul Pluzhnikov

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diff --git a/gdb/configure.ac b/gdb/configure.ac
index 698fc7b834..e1f630cd38 100644
--- a/gdb/configure.ac
+++ b/gdb/configure.ac
@@ -732,7 +732,7 @@ AC_DEFUN([AC_TRY_LIBPYTHON],
   save_CPPFLAGS=$CPPFLAGS
   save_LIBS=$LIBS
   CPPFLAGS="$CPPFLAGS $new_CPPFLAGS"
-  LIBS="$LIBS $new_LIBS"
+  LIBS="$new_LIBS $LIBS"
   found_usable_python=no
   AC_LINK_IFELSE(AC_LANG_PROGRAM([[#include "Python.h"]],
                                  [[Py_Initialize ();]]),
@@ -922,19 +922,19 @@ else
   elif test "${have_python_config}" != failed; then
     if test "${have_libpython}" = no; then
       AC_TRY_LIBPYTHON(python2.7, have_libpython,
-                       ${python_includes}, "${python_libs} -lpython2.7")
+                       ${python_includes}, "-lpython2.7 ${python_libs}")
     fi
     if test "${have_libpython}" = no; then
       AC_TRY_LIBPYTHON(python2.6, have_libpython,
-                       ${python_includes}, "${python_libs} -lpython2.6")
+                       ${python_includes}, "-lpython2.6 ${python_libs}")
     fi
     if test ${have_libpython} = no; then
       AC_TRY_LIBPYTHON(python2.5, have_libpython,
-                       ${python_includes}, "${python_libs} -lpython2.5")
+                       ${python_includes}, "-lpython2.5 ${python_libs}")
     fi
     if test ${have_libpython} = no; then
       AC_TRY_LIBPYTHON(python2.4, have_libpython,
-                       ${python_includes}, "${python_libs} -lpython2.4")
+                       ${python_includes}, "-lpython2.4 ${python_libs}")
     fi
   fi
   if test "${have_libpython}" = python2.7 -o "${have_libpython}" = python27; then
diff --git a/gdb/python/python-config.py b/gdb/python/python-config.py
index c2b2969c39..0d38ed50c0 100644
--- a/gdb/python/python-config.py
+++ b/gdb/python/python-config.py
@@ -58,12 +58,11 @@ for opt in opt_flags:
         print (to_unix_path(' '.join(flags)))
 
     elif opt in ('--libs', '--ldflags'):
-        libs = []
+        libs = ['-lpython'+pyver + abiflags]
         if getvar('LIBS') is not None:
             libs.extend(getvar('LIBS').split())
         if getvar('SYSLIBS') is not None:
             libs.extend(getvar('SYSLIBS').split())
-        libs.append('-lpython'+pyver + abiflags)
         # add the prefix/lib/pythonX.Y/config dir, but only if there is no
         # shared library in prefix/lib/.
         if opt == '--ldflags':