This commit adds support for timer interrupts, replacing the busy loop
that was used before. It is perhaps the most simple interrupt to
implement and should serve as the basis for further interrupt support in
RISC-V.
Now that we use LLVM 9, RISC-V support in LLVM has far fewer bugs and we
can avoid the GNU toolchain.
* replace GNU linker with lld
* replace GCC with clang
Additionally, RISC-V was promoted to stable so it can be enabled by
default in CI.
The .sdata and .sbss sections are created by the compiler, but were not
present in the linker script. That means that the linker put them after
all other data/bss section, which happens to be where the heap also
resides.
This commit adds the .sdata and .sbss sections to the linker script,
which gets the blinky examples to work again on RISC-V.
This prevents it from being of type PROGBITS in lld 9, it should always
be NOBITS. It should fix the following error in lld 9:
ROM segments are non-contiguous
