Perfprofd: Rewrite perf invocation arg generation

Use a vector to prepare for variable (and possibly long) list of
arguments. Move arg vector preparation to before the fork to avoid
undefined behavior.

Bug: 110555909
Test: mmma system/extras/perfprofd
Test: perfprofd_test
Change-Id: I71ab88194edbf8e9c58bbfd40a327accb1da0e47
1 file changed