[build] Do not strip shared libs if devtools shall be installed.

Stripping has some bad side effects for dev tools. For example, stripping libpthread.so.0 (and libthread_db.so.1 ?) breaks gdb's ability to debug  threads.

GDB output (with "set debug libthread-db 1"):

Trying host libthread_db library: libthread_db.so.1.
Host libthread_db.so.1 resolved to: /lib/libthread_db.so.1.
td_ta_new failed: application not linked with libthread
Trying host libthread_db library: /lib/libthread_db.so.1.
td_ta_new failed: application not linked with libthread
thread_db_load_search returning 0
warning: Unable to find libthread_db matching inferior's thread library, thread debugging will not be available.