[UNIKRAFT PATCH v2 1/3] build: Configure the compiler from command line

[Vlad-Andrei Badoiu <vlad_andrei.badoiu@xxxxxx>]

By default, the compiler is GCC. Use COMPILER=clang with make to configure the 
compiler as CLANG.

Signed-off-by: Alice Suiu <alicesuiu17@xxxxxxxxx>
Signed-off-by: Vlad-Andrei Badoiu <vlad_andrei.badoiu@xxxxxx>
---
 Makefile | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index 1f309b7d..b3ba38c4 100644
--- a/Makefile
+++ b/Makefile
@@ -544,11 +544,20 @@ ifneq ("$(origin CROSS_COMPILE)","undefined")
 CONFIG_CROSS_COMPILE := $(CROSS_COMPILE:"%"=%)
 endif
 
+# Use 'make COMPILER=clang' to compile with clang
+ifeq ("$(origin COMPILER)", "command line")
+  CONFIG_COMPILER := $(COMPILER)
+endif
+ifndef CONFIG_COMPILER
+  CONFIG_COMPILER = gcc
+endif
+
+
 $(eval $(call verbose_include,$(CONFIG_UK_BASE)/arch/$(UK_FAMILY)/Compiler.uk))
 
 # Make variables (CC, etc...)
-LD             := $(CONFIG_CROSS_COMPILE)gcc
-CC             := $(CONFIG_CROSS_COMPILE)gcc
+LD             := $(CONFIG_CROSS_COMPILE)$(CONFIG_COMPILER)
+CC             := $(CONFIG_CROSS_COMPILE)$(CONFIG_COMPILER)
 CPP            := $(CC)
 CXX            := $(CPP)
 GOC            := $(CONFIG_CROSS_COMPILE)gccgo-7
-- 
2.27.0