unix/Makefile: Move coverage.c and coveragecpp.cpp to coverage variant.

So that g++ is not needed to build a non-coverage unix variant.

Signed-off-by: Damien George <damien@micropython.org>

ports/unix/Makefile

@@ -220,7 +220,7 @@ SRC_MOD += modjni.c
 endif
 
 # source files
-SRC_C = \
+SRC_C += \
 	main.c \
 	gccollect.c \
 	unix_mphal.c \
@@ -232,7 +232,6 @@ SRC_C = \
 	modtime.c \
 	moduselect.c \
 	alloc.c \
-	coverage.c \
 	fatfs_port.c \
 	mpbthciport.c \
 	mpbtstackport_common.c \
@@ -249,7 +248,6 @@ LIB_SRC_C += $(addprefix lib/,\
 	)
 
 SRC_CXX += \
-	coveragecpp.cpp \
 	$(SRC_MOD_CXX)
 
 OBJ = $(PY_O)

ports/unix/variants/coverage/mpconfigvariant.mk

@@ -19,3 +19,6 @@ MICROPY_ROM_TEXT_COMPRESSION = 1
 MICROPY_VFS_FAT = 1
 MICROPY_VFS_LFS1 = 1
 MICROPY_VFS_LFS2 = 1
+
+SRC_C += coverage.c
+SRC_CXX += coveragecpp.cpp