feat(build): propagate compiler flags from files to toolchain.cmake

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.

components/riscv/project_include.cmake

@@ -1,5 +0,0 @@
-# avoid esp-clang "unused-command-line-argument" warning
-if(NOT (CMAKE_C_COMPILER_ID MATCHES "Clang") )
-    set(compile_options "-nostartfiles")
-    idf_build_set_property(COMPILE_OPTIONS "${compile_options}" APPEND)
-endif()