Fix multilib builds with --use-bootstrap-image

When building an i?86 package (with i?86 chroot config) on an x86_64
host, we report to kernel that we work in 32 bit mode (using the
'/bin/setarch'-like condPersonality() call).  This is completely OK and
desired for the build (target) chroot, but not for the bootstrap chroot
which is generated from a container image.

The container image has always a host-native arch (unless there's a
configuration error).  So the pre-installed packages are x86_64.
When we want to install additional packages there (typically to provide
the 'dnf builddep' command in bootstrap), and we do that using the
package manager already installed in bootstrap image (no package manager
on host is required!), the package manager is confused by the 32-bit
mode and resolves '$basearch' into 'i386' instead of 'x86_64'.  So we
need to switch back to 64-bit mode (in a subprocess, preexec_fn).

Note that a late call to `os.uname()` would be confused by the
condPersonality() call.  So newly we rather remember the 'host_arch' at
the beginning in config_opts, before the initial call to
condPersonality().

Fixes: #1110

mock/py/mock.py

@@ -521,7 +521,7 @@ def check_arch_combination(target_arch, config_opts):
         legal = config_opts['legal_host_arches']
     except KeyError:
         return
-    host_arch = os.uname()[-1]
+    host_arch = config_opts['host_arch']
     if (host_arch not in legal) and not config_opts['forcearch']:
         log.info("Unable to build arch %s natively on arch %s. Setting forcearch to use software emulation.",
                  target_arch, host_arch)

mock/py/mockbuild/config.py

@@ -62,6 +62,7 @@ def setup_default_config_opts():
     config_opts['chroothome'] = '/builddir'
     config_opts['log_config_file'] = 'logging.ini'
     config_opts['rpmbuild_timeout'] = 0
+    config_opts['host_arch'] = os.uname()[-1]
     config_opts['chrootuid'] = os.getuid()
     try:
         config_opts['chrootgid'] = grp.getgrnam("mock")[2]

mock/py/mockbuild/package_manager.py

@@ -270,9 +270,18 @@ def _execute_mounted(self, *args, **kwargs):
                 # either it does not support --installroot (microdnf) or
                 # it is bootstrap image made by container with incomaptible dnf/rpm
                 if not self.support_installroot or self.is_bootstrap_image:
+
+                    personality = kwargs.pop("personality", None)
+                    if self.is_bootstrap_image:
+                        # Multilib fix - the in-bootstrap package manager needs
+                        # to know what to resolve $buildarch, wither the 32 or
+                        # 64-bit variant.  But with bootstrap image, we always
+                        # use the image of the hosts native architecture!
+                        personality = self.config['host_arch']
+
                     out = util.do(invocation, env=env,
                                   chrootPath=self.buildroot.make_chroot_path(),
-                                  **kwargs)
+                                  personality=personality, **kwargs)
                 elif self.bootstrap_buildroot is None:
                     out = util.do(invocation, env=env,
                                   **kwargs)