pthread double free when run through libroot_debug.so

[kallisti5]

Our pthread implementation has a minor memory access bug somewhere.

To reproduce:

Download a simple pthread example:
  http://www.cs.ucsb.edu/~tyang/class/pthreads/code_sgi/p_hello.c

Compile it:
  gcc p_hello.c

Run it under libroot_debug.so:
  LD_PRELOAD=/system/lib/libroot_debug.so ./a.out 5

[kallisti5]

Noticed when running mesa through libroot_debug.so. memory violation happens with any pthread application.

[jessicah]

It might actually be our IO layer that's broken/not thread safe.

[korli]

Fixed in hrev48949, using pthread mutexes for libc locking.