Move version files out of extern folder

The folder extern is reserved for external contributions, not common
files.

Signed-off-by: Antonio Niño Díaz <antonio_nd@outlook.com>

Makefile

@@ -58,7 +58,7 @@ rgbasm_obj := \
 	src/asm/symbol.o \
 	src/extern/err.o \
 	src/extern/utf8decoder.o \
-	src/extern/version.o
+	src/version.o
 
 src/asm/asmy.h: src/asm/asmy.c
 src/asm/locallex.o src/asm/globlex.o src/asm/lexer.o: src/asm/asmy.h
@@ -76,7 +76,7 @@ rgblink_obj := \
 	src/link/script.o \
 	src/link/symbol.o \
 	src/extern/err.o \
-	src/extern/version.o
+	src/version.o
 
 src/link/parser.h: src/link/parser.c
 src/link/lexer.o: src/link/parser.h
@@ -84,14 +84,14 @@ src/link/lexer.o: src/link/parser.h
 rgbfix_obj := \
 	src/fix/main.o \
 	src/extern/err.o \
-	src/extern/version.o
+	src/version.o
 
 rgbgfx_obj := \
 	src/gfx/gb.o \
 	src/gfx/main.o \
 	src/gfx/makepng.o \
 	src/extern/err.o \
-	src/extern/version.o
+	src/version.o
 
 rgbasm: ${rgbasm_obj}
 	$Q${CC} ${REALCFLAGS} -o $@ ${rgbasm_obj} -lm