build: Add LLVM_TARGET_ARCH

Rustc uses the LLVM format for specifying the cross
compiler target: <arch><sub>-<vendor>-<sys>-<abi>.
This is different from GCC, in order to not have
to mantain a translation script, we provide the user
with an option to specify himself the target via
LLVM_TARGET_ARCH which is similar to CROSS_COMPILE.

Signed-off-by: Vlad-Andrei Badoiu <[email protected]>
Reviewed-by: Simon Kuenzer <[email protected]>
Tested-by: Unikraft CI <[email protected]>
GitHub-Pull-Request: unikraft#241

Author: vladandrew

Config.uk

@@ -168,6 +168,15 @@ config CROSS_COMPILE
 		need to set this unless you want the configured build
 		directory to select the cross-compiler automatically.
 
+
+config LLVM_TARGET_ARCH
+	string "Custom cross-compiler LLVM target (optional)"
+	help
+		Same as running 'make LLVM_TARGET_ARCH=target' but stored for
+		default make runs in this build directory.  You don't
+		need to set this unless you want the configured build
+		directory to select the cross-compiler automatically.
+		This is used for LLVM based compilers such as clang or rustc.
 #config PARALLEL_JOBS
 #	int "Number of jobs to run simultaneously (0 for auto)"
 #	default "0"

Makefile

@@ -515,6 +515,7 @@ ifeq ($(sub_make_exec), 1)
 ifeq ($(UK_HAVE_DOT_CONFIG),y)
 # Hide troublesome environment variables from sub processes
 unexport CONFIG_CROSS_COMPILE
+unexport CONFIG_LLVM_TARGET_ARCH
 unexport CONFIG_COMPILER
 #unexport CC
 #unexport LD
@@ -548,6 +549,10 @@ ifneq ("$(origin CROSS_COMPILE)","undefined")
 CONFIG_CROSS_COMPILE := $(CROSS_COMPILE:"%"=%)
 endif
 
+ifneq ("$(origin LLVM_TARGET_ARCH)","undefined")
+CONFIG_LLVM_TARGET_ARCH := $(LLVM_TARGET_ARCH:"%"=%)
+endif
+
 ifneq ("$(origin COMPILER)","undefined")
 	CONFIG_COMPILER := $(COMPILER:"%"=%)
 else