build system: General refactoring
The original goal here was to support setting different COMPONENT_INCLUDEDIRS/COMPONENT_LDFLAGS based on sdkconfig. It's turned into a general refactor.
* The `get_variable` target & associated macros have been replaced with a target that generates a makefile snippet for each component (inside the build directory), and includes these in the project make pass. This improves build speed ( "no-op" `make all` on my system is down from 1.43s (wall) / 0.55s (CPU) to 0.49s (wall) / 0.23s (CPU) due to not forking as many processes) and also makes the builds more debuggable, as you can go and look at the component_project_vars.mk files in the build directory to see what paths are being added where.
* Including component_common.mk from component.mk is no longer necessary (and prints a deprecation warning). Instead, component.mk is included from inside a wrapper makefile. This allows default variables and project configuration to be loaded before component.mk begins, and removes the need to split makefile statements arbitrarily between "before including component_common" and "after including component_common", with which goes where depending on internals of the build system. Part-fix for TW#8017.
* Rewrote build system docs to reflect these details and also clarify some other points, add more ReST structure. Fixes other issues raised in TW#8017.
* Should be backwards compatible with existing components. The only difference I know is the deprecation warning when including component_common.mk.
Adds one new failure case: because some paths are encoded in the generated component_project_vars.mk files then reorganising the component directory structure (but not modifying any other files or menuconfig) may cause a partial build to fail and require a `make clean`. Moving the whole project directory, whole build directory, or whole ESP-IDF directory will not trigger this. This failure case should only ever cause a build error, not incorrect build output.
See merge request !188
Per-CPU interrupt handlers and args
Up to now, the interrupt handlers and args were shared between CPUs, that is, if you set an interrupt handler on CPU0, CPU1 would invoke the same interrupt handler on that interrupt. This code gives every CPU its own space for interrupt handlers.
See merge request !192
NVS examples
Add two examples for working with NVS.
One is reading and writing an integer value, another is reading and writing a blob.
See merge request !194
