Separate BUILD compiler from HOST compiler

[gatuno]

Type of issue

Feature Request

Description

When using the current Makefile in crust, it may be hard to cross-compile for another platform, for example, imagine that you are on a amd64 host building an image for armv8a and using also the or1k compiler. The current definition at the main Makefile uses HOSTCC = cc, which could use the amd64 host's gcc, and not the armv8a that is needed.

My suggestion is to change the main Makefile to:

OR1K_COMPILE    ?= or1k-linux-musl-
AR       = $(OR1K_COMPILE)gcc-ar
CC       = $(OR1K_COMPILE)gcc
CPP      = $(OR1K_COMPILE)cpp
OBJCOPY      = $(OR1K_COMPILE)objcopy

CROSS_COMPILE ?= 
HOSTAR       = $(CROSS_COMPILE)ar
HOSTCC       = $(CROSS_COMPILE)cc

Using the current Makefile would need to change the PATH variable to include first the cross-compilers (like the armv8a) and changing the Makefile would allow to specify when invoking the make.

[smaeul]

In the past I've suggested using make HOSTCC=aarch64-linux-musl-gcc tools, but Kconfig is also built with HOSTCC, so this now breaks if Kconfig isn't already built. I think what I want to do is use HOSTCC for the tools, and a new variable BUILDCC for Kconfig or other tools used during the build process. Then HOSTCC could default to an ARM/AArch64 toolchain.

[smaeul]

This would require adding more rules to the top-level Makefile, and a new buildprogs Kbuild rule.

[smaeul]

Fixed by 9e417af83b35f6882d3bbc2e1e183f9893c37158