updated makefiles for clang

practical_work/forces/Makefile

-CC=gcc
-OPTS=-g -O3 -Wall -Wextra -fsanitize=address -fsanitize=leak -std=c11
-LINK=-lm -lasan
+CC=clang
+OPTS=-g -O3 -Wall -Wextra -fsanitize=address -std=c11
+LINK=-lm -fsanitize=address
 
 main: main.o particle.o ../vec2/util.o ../vec2/vec2.o
 	make -C ../vec2

practical_work/vec2/Makefile

-CC=gcc
+CC=clang
 OPTS=-g -O3 -Wall -Wextra
 LINK=-lm
 

practical_work/vec2/tests/Makefile

-CC=gcc
+CC=clang
 OPTS=-g -O3 -Wall -Wextra
 LINK=-lm