package/rustc: fix the riscv64gc architecture handling

riscv64gc was made available for BR2_riscv, but RISC-V can be 32-bit
or 64-bit, so we need to restrict it to BR2_RISCV_64. There's no need
to keep the BR2_riscv dependency, as BR2_RISCV_64 can only be true
when BR2_riscv is true.

Also, BR2_PACKAGE_HOST_RUSTC_ARCH needs to be set to riscv64gc to
allow rust-bin to download its pre-compiled standard library
correctly.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/rustc/Config.in.host

@@ -49,7 +49,7 @@ config BR2_PACKAGE_HOST_RUSTC_TARGET_TIER2_HOST_TOOLS_PLATFORMS
 	default y if BR2_powerpc64le && BR2_TOOLCHAIN_USES_GLIBC
 	# riscv64gc-unknown-linux-gnu
 	# "g" stands for imafd, and we also need "c".
-	default y if BR2_riscv && BR2_RISCV_ISA_RVI && BR2_RISCV_ISA_RVM && \
+	default y if BR2_RISCV_64 && BR2_RISCV_ISA_RVI && BR2_RISCV_ISA_RVM && \
 			BR2_RISCV_ISA_RVA && BR2_RISCV_ISA_RVF && \
 			BR2_RISCV_ISA_RVD && BR2_RISCV_ISA_RVC && \
 			BR2_TOOLCHAIN_USES_GLIBC
@@ -104,6 +104,7 @@ config BR2_PACKAGE_HOST_RUSTC_ARCH
 	string
 	default "armv5te" if BR2_ARM_CPU_ARMV5
 	default "armv7"  if BR2_ARM_CPU_ARMV7A
+	default "riscv64gc" if BR2_RISCV_64
 	default BR2_ARCH
 
 config BR2_PACKAGE_HOST_RUSTC_ABI