[Bug target/97329] POWER9 default cache and line sizes appear to be wrong

["kip at thevertigo dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97329

--- Comment #7 from Kip Warner <kip at thevertigo dot com> ---
So it looks like even with GCC 11 in trunk it's still sometimes wrong on
power9.

Wrong L2 cache size when no -mcpu specified:

$ gcc -Q --help=param | grep -i cache
  --param=l1-cache-line-size=           128
  --param=l1-cache-size=                32
  --param=l2-cache-size=                256

Correct when manually specifying native (power9) cpu:

$ gcc -Q -mcpu=native --help=param | grep -i cache
  --param=l1-cache-line-size=           128
  --param=l1-cache-size=                32
  --param=l2-cache-size=                512

Correct when manually specifying power9 cpu:

$ gcc -Q -mcpu=power9 --help=param | grep -i cache
  --param=l1-cache-line-size=           128
  --param=l1-cache-size=                32
  --param=l2-cache-size=                512

Wrong L2 cache size when powerpc64le is selected in place of power9:

$ gcc -Q -mcpu=powerpc64le --help=param | grep -i cach
  --param=l1-cache-line-size=           128
  --param=l1-cache-size=                32
  --param=l2-cache-size=                256

Looks like this might be a clue. GCC did not identify the host/build/target as
power9 automatically:

$ gcc -dumpmachine
powerpc64le-unknown-linux-gnu

I built it from trunk last night on a power9 machine. I've attached my
config.log.

$ gcc --version
gcc (GCC) 11.0.0 20201008 (experimental)
(...)