bpo-36361: Generate correct pyconfig.h when cross-compiling

[xdegaye]

When cross-compiling and the CONFIG_SITE environment variable is unset or empty, configure copies the executables, results of the build of the AC_RUN_IFELSE test programs in configure.ac, to the build/run_ifelse_cvs directory.

The Misc/build_config_site.sh script may be run then to create a config.site file when invoked with one of the parameters as a path to a shell script that transfers an executable to the platform, target of the cross-compilation, and runs it on this platform.

A second run of 'configure' with the CONFIG_SITE environment variable set to the absolute path of this config.site file allows configuring the Python build with the correct cache values for this platform.

https://bugs.python.org/issue36361

[xdegaye]

For example, on Android arm64 at API 24, the config.site file is:

# This script has been generated by build_config_site.sh from the following
# list of cache values handled by AC_RUN_IFELSE macros as found
# in configure.ac:
#
#    ac_cv_aligned_required
#    ac_cv_broken_mbstowcs
#    ac_cv_broken_nice
#    ac_cv_broken_poll
#    ac_cv_broken_sem_getvalue
#    ac_cv_buggy_getaddrinfo
#    ac_cv_c_bigendian
#    ac_cv_computed_gotos
#    ac_cv_have_chflags
#    ac_cv_have_lchflags
#    ac_cv_have_size_t_format
#    ac_cv_kpthread
#    ac_cv_kthread
#    ac_cv_posix_semaphores_enabled
#    ac_cv_pthread
#    ac_cv_pthread_is_default
#    ac_cv_pthread_system_supported
#    ac_cv_rshift_extends_sign
#    ac_cv_wchar_t_signed
#    ac_cv_working_tzset
#    ac_cv_x87_double_rounding
#    have_glibc_memmove_bug
#
# The list may be used to verify that this config.site file has not become
# stale in the case of addition of new cache values in configure.ac.
#
# The script sets the following cache values that have been found different
# from the pessimistic default values set by AC_RUN_IFELSE, after running the
# executable on the target machine:


  ac_cv_pthread_is_default=yes
  ac_cv_kthread=no
  ac_cv_pthread=no

ac_cv_aligned_required=no
ac_cv_pthread_system_supported=yes
ac_cv_have_chflags=no
ac_cv_have_lchflags=no
ac_cv_buggy_getaddrinfo=no
ac_cv_posix_semaphores_enabled=no
ac_cv_wchar_t_signed=no
ac_cv_c_bigendian=no
ac_cv_working_tzset=yes
ac_cv_have_size_t_format=yes
ac_cv_computed_gotos=yes
have_glibc_memmove_bug=no

[xdegaye]

The helper script used by Misc/build_config_site.sh to create the above config.site file for Android running on an emulator or a device, is:

#! /bin/sh
#
#   usage: adb_push_exec.sh /path/to/executable
#
# Use adb to push an executable on an Android emulator or device and
# to run the executable.

# The name of the executable using variable substitution instead of basename.
executable=${1##*/}

adb=$ANDROID_SDK_ROOT/platform-tools/adb
tmpdir=/data/local/tmp

$adb push $1 $tmpdir >/dev/null 2>&1
$adb shell $tmpdir/$executable
status=$?
$adb shell rm $tmpdir/$executable
exit $status