Support AMD Opteron

I'm unable to run rr 3.0.0 on a js shell.

$ rr record /home/gkwong/shell-cache/js-dbg-64-prof-nsprBuild-linux-3cda3997f45d/js-dbg-64-prof-nsprBuild-linux-3cda3997f45d
rr: Saving the execution of /home/gkwong/shell-cache/js-dbg-64-prof-nsprBuild-linux-3cda3997f45d/js-dbg-64-prof-nsprBuild-linux-3cda3997f45d' to trace directory/home/gkwong/.rr/js-dbg-64-prof-nsprBuild-linux-3cda3997f45d-2'.
[FATAL /home/roc/rr/rr/src/PerfCounters.cc:131:get_cpu_microarch() errno: 0 'Success']
-> CPU 0xf10 unknown.
Aborted

I'm using a 32-core (as seen from the OS) AMD CPU, e.g.:

processor : 0
vendor_id : AuthenticAMD
cpu family : 21
model : 1
model name : AMD Opteron(TM) Processor 6272
stepping : 2
microcode : 0x600063d
cpu MHz : 2100.000
cache size : 2048 KB
physical id : 0
siblings : 16
core id : 0
cpu cores : 8
apicid : 32
initial apicid : 0
fpu : yes
fpu_exception : yes
cpuid level : 13
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm constant_tsc rep_good nopl nonstop_tsc extd_apicid amd_dcm aperfmperf pni pclmulqdq monitor ssse3 cx16 sse4_1 sse4_2 popcnt aes xsave avx lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs xop skinit wdt lwp fma4 nodeid_msr topoext perfctr_core perfctr_nb arat cpb hw_pstate npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasid decodeassists pausefilter pfthreshold vmmcall
bogomips : 4189.45
TLB size : 1536 4K pages
clflush size : 64
cache_alignment : 64
address sizes : 48 bits physical, 48 bits virtual
power management: ts ttp tm 100mhzsteps hwpstate cpb

and can be seen here too: http://pastebin.mozilla.org/8548446

The failure is reported at rr/src/PerfCounters.cc:131 in get_cpu_microarch(); start there and inspect how CPU 0xf10 is identified. Reproduce with the AMD Opteron details in the report and verify that rr no longer aborts on this processor.