[roll third_party/pigweed] pw_preprocessor: Add internal Cortex-M arch defines

Instead of forking build rules to be arch specific, which does not
scale well with the number of CortexM arches, use a common place to
determine the arch macros which can be used by other macros.

Note that these defines are private and internal to Pigweed and
should not be used by downstream projects, they are expected to
be moved and renamed in the near future.

The defines default to the format used by CMSIS, GCC, Clang, etc.
but they follow a module compile time configuration paradigm so
different toolchains can also make the following defines work:
- _PW_ARCH_ARM_V6M
- _PW_ARCH_ARM_V7M
- _PW_ARCH_ARM_V7EM
- _PW_ARCH_ARM_V8M_BASELINE
- _PW_ARCH_ARM_V8M_MAINLINE
- _PW_ARCH_ARM_V8_1M_MAINLINE

Lastly a helper is provided if any of the above have a value of 1:
- _PW_ARCH_ARM_CORTEX_M

Also updates pw_boot_cortex_m, pw_cpu_exception_cortex_m, and
pw_interrupt_cortex_m to use this source of architecture selection
deprecating the previously independent build targets.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/75540

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: d56a6386ca2422c..242a27cc3b30338
Roller-URL: https://ci.chromium.org/b/8825399273141730433
Cq-Cl-Tag: roller-builder:pigweed-sample-project-roller
Cq-Cl-Tag: roller-bid:8825399273141730433
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I91384c884e4a1a8eaf0e414af0bf8001b48622d2
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/sample_project/+/77743
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index d56a638..242a27c 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit d56a6386ca2422ce7ee50f0e917e5b2b6e100257
+Subproject commit 242a27cc3b3033898b4ead86d16dfef765cfe5b4