Set default visibility on art_sigsegv_fault.

Set default visibility on art_sigsegv_fault.

libart.so is built with flag -fvisibility=protected
which complicates setting breakpoints on art_sigsegv_fault.
According to the GCC manual "Protected visibility indicates
that the symbol will be placed in the dynamic symbol table,
but that references within the defining module will bind
to the local symbol.". This implies that a breakpoint on
a protected symbol will not be hit.

Without this change gdbclient with ART debugging enabled
doesn't break at art_sigsegv_fault as expected.

Bonus build fix included (commit c37769b6) :

Fix lint error.

Blank line at the start of a code block.

(cherry picked from commit f775bab533cd385c00ee30b56bdcb6f962fc5239)
(cherry picked from commit c37769b63faf7b120a6ed80f5cfb92667f5090c4)

bug: 21893559

Change-Id: Ie388f027f717a7bd2351a0163a38e50d3acbba8f