pw_cpu_exception_cortex_m: Move armv7m->cortex_m

Moves the armv7m implementation of pw_cpu_exception to
pw_cpu_exception_cortex_m since much of the logic can be shared between
ARMv8-M and ARMv7-M. Symbol names are also updated to reflect current
naming style for extern "C" symbols. Old names will be removed in
pwrev/31060.

Warning, symbol renames are breaking!
pw_CpuExceptionEntry -> pw_cpu_exception_Entry
pw_CpuExceptionDefaultHandler -> pw_cpu_exception_DefaultHandler

Change-Id: I7ab99ac7637c436ba959d7546043090c66fe4215
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/30922
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
Reviewed-by: Ewout van Bekkum <ewout@google.com>
Pigweed-Auto-Submit: Armando Montanez <amontanez@google.com>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 20870ee..9447bda 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -36,7 +36,7 @@
 add_subdirectory(pw_chrono_stl EXCLUDE_FROM_ALL)
 add_subdirectory(pw_containers EXCLUDE_FROM_ALL)
 add_subdirectory(pw_cpu_exception EXCLUDE_FROM_ALL)
-add_subdirectory(pw_cpu_exception_armv7m EXCLUDE_FROM_ALL)
+add_subdirectory(pw_cpu_exception_cortex_m EXCLUDE_FROM_ALL)
 add_subdirectory(pw_hdlc EXCLUDE_FROM_ALL)
 add_subdirectory(pw_kvs EXCLUDE_FROM_ALL)
 add_subdirectory(pw_log EXCLUDE_FROM_ALL)