Add Phobos compilation metrics to the perf bot

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DMD perf check

Metric	Base	PR	delta
compile hello.d (instr)	215.6 M	215.6 M	0.00%
compile hello.d -O (instr)	234.1 M	234.1 M	0.00%
compile Phobos (instr)	5,079.1 M	5,079.1 M	-0.00%
dmd binary size (stripped)	6.87 MB	6.87 MB	0.00%
hello binary size	0.72 MB	0.72 MB	0.00%
peak RSS (compile hello.d)	44 MB	44 MB	-0.04%
peak RSS (compile Phobos)	634 MB	634 MB	+0.03%