Bug 1664567 - Set `MOZ_OBJDIR` in builder scripts for CI r=glandium

Without setting this variable, the call to `mach python` in `taskcluster/scripts/builder/build-linux.sh` will create a `virtualenv` in the default location -- on Linux in CI, that's `obj-x86_64-pc-linux-gnu`. Everything else about the build is going to end up in `obj-build`, so just set `MOZ_OBJDIR` appropriately to point to that directory.

Doing so enables us to land bug 1663755, as it causes the logic added to `symbols_archive.py` as part of bug 1654994 to behave as expected.

Differential Revision: https://phabricator.services.mozilla.com/D89975

taskcluster/scripts/builder/build-l10n.sh

@@ -28,6 +28,7 @@ echo "running as" $(id)
 : MOZ_SCM_LEVEL                 ${MOZ_SCM_LEVEL:=1}
 
 : WORKSPACE                     ${WORKSPACE:=/builds/worker/workspace}
+: MOZ_OBJDIR                    ${MOZ_OBJDIR:=$WORKSPACE/obj-build}
 
 set -v
 
@@ -66,6 +67,8 @@ fi
 # entirely effective.
 export TOOLTOOL_CACHE
 
+export MOZ_OBJDIR
+
 config_path_cmds=""
 for path in ${MOZHARNESS_CONFIG_PATHS}; do
     config_path_cmds="${config_path_cmds} --extra-config-path ${GECKO_PATH}/${path}"

taskcluster/scripts/builder/build-linux.sh

@@ -27,6 +27,7 @@ echo "running as" $(id)
 : MH_BUILD_POOL                 ${MH_BUILD_POOL:=staging}
 
 : WORKSPACE                     ${WORKSPACE:=/builds/worker/workspace}
+: MOZ_OBJDIR                    ${MOZ_OBJDIR:=$WORKSPACE/obj-build}
 
 set -v
 
@@ -81,6 +82,8 @@ fi
 # entirely effective.
 export TOOLTOOL_CACHE
 
+export MOZ_OBJDIR
+
 config_path_cmds=""
 for path in ${MOZHARNESS_CONFIG_PATHS}; do
     config_path_cmds="${config_path_cmds} --extra-config-path ${GECKO_PATH}/${path}"

taskcluster/scripts/builder/repackage.sh

@@ -23,6 +23,7 @@ echo "running as" $(id)
 : MOZ_SCM_LEVEL                 ${MOZ_SCM_LEVEL:=1}
 
 : WORKSPACE                     ${WORKSPACE:=/builds/worker/workspace}
+: MOZ_OBJDIR                    ${MOZ_OBJDIR:=$WORKSPACE/obj-build}
 
 set -v
 
@@ -62,6 +63,8 @@ fi
 # entirely effective.
 export TOOLTOOL_CACHE
 
+export MOZ_OBJDIR
+
 config_path_cmds=""
 for path in ${MOZHARNESS_CONFIG_PATHS}; do
     config_path_cmds="${config_path_cmds} --extra-config-path ${GECKO_PATH}/${path}"