ZEN: more uarches for kernel 5.8+

WARNING
This patch works with all gcc versions 9.0+ and with kernel version 5.8+ and should
NOT be applied when compiling on older versions of gcc due to key name changes
of the march flags introduced with the version 4.9 release of gcc.[1]

FEATURES
This patch adds additional CPU options to the Linux kernel accessible under:
 Processor type and features  --->
  Processor family --->

With the release of gcc 11.0, several generic 64-bit levels are offered which
are good for supported Intel or AMD CPUs:
• x86-64-v2
• x86-64-v3
• x86-64-v4

Users of glibc 2.33 and above can see which level is supported by current
hardware by running:
  /lib/ld-linux-x86-64.so.2 --help | grep supported

Alternatively, compare the flags from /proc/cpuinfo to this list.[2]

CPU-specific microarchitectures include:
• AMD Improved K8-family
• AMD K10-family
• AMD Family 10h (Barcelona)
• AMD Family 14h (Bobcat)
• AMD Family 16h (Jaguar)
• AMD Family 15h (Bulldozer)
• AMD Family 15h (Piledriver)
• AMD Family 15h (Steamroller)
• AMD Family 15h (Excavator)
• AMD Family 17h (Zen)
• AMD Family 17h (Zen 2)
• AMD Family 19h (Zen 3)†
• Intel Silvermont low-power processors
• Intel Goldmont low-power processors (Apollo Lake and Denverton)
• Intel Goldmont Plus low-power processors (Gemini Lake)
• Intel 1st Gen Core i3/i5/i7 (Nehalem)
• Intel 1.5 Gen Core i3/i5/i7 (Westmere)
• Intel 2nd Gen Core i3/i5/i7 (Sandybridge)
• Intel 3rd Gen Core i3/i5/i7 (Ivybridge)
• Intel 4th Gen Core i3/i5/i7 (Haswell)
• Intel 5th Gen Core i3/i5/i7 (Broadwell)
• Intel 6th Gen Core i3/i5/i7 (Skylake)
• Intel 6th Gen Core i7/i9 (Skylake X)
• Intel 8th Gen Core i3/i5/i7 (Cannon Lake)
• Intel 10th Gen Core i7/i9 (Ice Lake)
• Intel Xeon (Cascade Lake)
• Intel Xeon (Cooper Lake)*
• Intel 3rd Gen 10nm++ i3/i5/i7/i9-family (Tiger Lake)*
• Intel 3rd Gen 10nm++ Xeon (Sapphire Rapids)‡
• Intel 11th Gen i3/i5/i7/i9-family (Rocket Lake)‡
• Intel 12th Gen i3/i5/i7/i9-family (Alder Lake)‡

Notes: If not otherwise noted, gcc >=9.1 is required for support.
       *Requires gcc >=10.1  †Required gcc >=10.3  ‡Required gcc >=11.0

It also offers to compile passing the 'native' option which, "selects the CPU
to generate code for at compilation time by determining the processor type of
the compiling machine. Using -march=native enables all instruction subsets
supported by the local machine and will produce code optimized for the local
machine under the constraints of the selected instruction set."[3]

Users of Intel CPUs should select the 'Intel-Native' option and users of AMD
CPUs should select the 'AMD-Native' option.

MINOR NOTES RELATING TO INTEL ATOM PROCESSORS
This patch also changes -march=atom to -march=bonnell in accordance with the
gcc v4.9 changes. Upstream is using the deprecated -match=atom flags when I
believe it should use the newer -march=bonnell flag for atom processors.[4]

It is not recommended to compile on Atom-CPUs with the 'native' option.[5] The
recommendation is to use the 'atom' option instead.

BENEFITS
Small but real speed increases are measurable using a make endpoint comparing
a generic kernel to one built with one of the respective microarchs.

See the following experimental evidence supporting this statement:
https://github.com/graysky2/kernel_gcc_patch

REQUIREMENTS
linux version >=5.8
gcc version >=9.0

ACKNOWLEDGMENTS
This patch builds on the seminal work by Jeroen.[6]

REFERENCES
1.  https://gcc.gnu.org/gcc-4.9/changes.html
2.  https://gitlab.com/x86-psABIs/x86-64-ABI/-/commit/77566eb03bc6a326811cb7e9
3.  https://gcc.gnu.org/onlinedocs/gcc/x86-Options.html#index-x86-Options
4.  https://bugzilla.kernel.org/show_bug.cgi?id=77461
5.  https://github.com/graysky2/kernel_gcc_patch/issues/15
6.  http://www.linuxforge.net/docs/linux/linux-gcc.php