Valgrind complains about ptls_fusion_is_supported_by_cpu

[huitema]

The code of the function is:

int ptls_fusion_is_supported_by_cpu(void)
{
    unsigned leaf1_ecx, leaf7_ebx;

    { /* GCC-specific code to obtain CPU features */
        unsigned leaf_cnt;
        __asm__("cpuid" : "=a"(leaf_cnt) : "a"(0) : "ebx", "ecx", "edx");
        if (leaf_cnt < 7)
            return 0;
        __asm__("cpuid" : "=c"(leaf1_ecx) : "a"(1) : "ebx", "edx");
        __asm__("cpuid" : "=b"(leaf7_ebx) : "a"(7), "c"(0) : "edx");
    }

    /* AVX2 */
    if ((leaf7_ebx & (1 << 5)) == 0)
        return 0;
    /* AES */
    if ((leaf1_ecx & (1 << 25)) == 0)
        return 0;
    /* PCLMUL */
    if ((leaf1_ecx & (1 << 1)) == 0)
        return 0;

    return 1;
}

Valgrind complains that the "Conditional jump or move depends on uninitialized value". This is very annoying, because the message will fill the valgrind logs when testing code that uses picotls.

I think this could be fixed by changing the declaration to unsigned leaf_cnt = 0;.