[line coverage] macros from system headers after `break` have wrong execution count

[whentojump]

How to reproduce it (Compiler explorer link):

cat > test.h << EOF
#define FOO x++
EOF
cat > test.c << EOF
#include <test.h>
int main(void)
{
    int x;
    for (int i=0; i<10; i++) {
        if (i==5)
            break;
        FOO;
        x++;
    }
    return 0;
}
EOF
clang -fprofile-instr-generate -fcoverage-mapping -isystem. test.c -o test
./test
llvm-profdata merge default.profraw -o default.profdata
llvm-cov show -instr-profile default.profdata test

Coverage report where line 8 and 9 are self-contradictory.

    1|       |#include <test.h>
    2|       |int main(void)
    3|      1|{
    4|      1|    int x;
    5|      6|    for (int i=0; i<10; i++) {
    6|      6|        if (i==5)
    7|      1|            break;
    8|      6|        FOO;
    9|      5|        x++;
   10|      5|    }
   11|      1|    return 0;
   12|      1|}

(Example reduced from https://github.com/mtoyoda/sl/blob/5.02/sl.c#L108 where getch is from #include <curses.h>)

Related: #78920