This change improves build consistency across external projects integrated
through CMake by ensuring that compiler flags defined in configuration files
are passed correctly to the toolchain. It covers the majority of use cases,
as external projects are typically also CMake-based. For projects that use
a custom build system, users will still need to specify the required flags
manually.
The esp_libc relies on the stdio implementation of the vfs component if
CONFIG_VFS_SUPPORT_IO is enabled. This is not an issue in cmakev1
because if the vfs component is not included in the project build, its
configuration is not available, and CONFIG_VFS_SUPPORT_IO is not set.
However, in cmakev2, the configuration for all components is available,
and the presence of some component configuration options does not
necessarily mean that the component is included in the project build.
When esp_libc is compiled without the vfs dependency but with
CONFIG_VFS_SUPPORT_IO enabled, the libc initialization will encounter a
panic due to a NULL pointer dereference (fp->_flags) in __swsetup_r, as
fopen in esp_libc_init_global_stdio will return NULL.
esp_stdio contains everything the old esp_vfs_console contained (the vfs stdio glue layer)
as well as other functionality related to stdio (previously referred to as console)
