improve valgrind client request support to include more targets

[andrewrk]

In debug builds, Zig memsets undefined memory to 0xaa, and then inserts a few instructions which provide metadata to Valgrind (or other tools that support this metadata, but I think it's only Valgrind currently). This makes it so that valgrind can detect uninitialized values:

pub fn main() u8 {
    var x: u32 = undefined;
    if (x == 1234) {
        return 1;
    } else {
        return 0;
    }
}

==25307== Conditional jump or move depends on uninitialised value(s)
==25307==    at 0x223C64: main (test2.zig:3)

I did a proof of concept of this with x86_64 (commit coming shortly). However Valgrind has support for more targets:

• i386 linux, darwin, mingw, solaris
• i386 windows
• x86_64 linux, darwin, mingw, solaris
• ppc32 linux
• ppc64be linux
• ppc64le linux
• arm linux
• arm64 linux
• s390x linux
• mips32 linux
• mips64 linux

[andrewrk]

I went ahead and turned this on by default for debug builds. Here's some timing tests I did:

behavior tests:
  no valgrind integration
  binary size: 1.2M
                  Name       Start         End    Duration     Percent
            Initialize      0.0000      0.0016      0.0016      0.0006
     Semantic Analysis      0.0016      0.6342      0.6326      0.2491
       Code Generation      0.6342      0.7451      0.1109      0.0436
      LLVM Emit Output      0.7451      2.4800      1.7349      0.6831
    Build Dependencies      2.4800      2.5077      0.0278      0.0109
             LLVM Link      2.5077      2.5398      0.0321      0.0126
                 Total      0.0000      2.5398      2.5398      1.0000
  
  
  valgrind integration
  binary size: 1.2M
                  Name       Start         End    Duration     Percent
            Initialize      0.0000      0.0016      0.0016      0.0006
     Semantic Analysis      0.0016      0.6332      0.6316      0.2440
       Code Generation      0.6332      0.7414      0.1082      0.0418
      LLVM Emit Output      0.7414      2.5310      1.7896      0.6915
    Build Dependencies      2.5310      2.5570      0.0260      0.0101
             LLVM Link      2.5570      2.5879      0.0309      0.0120
                 Total      0.0000      2.5879      2.5879      1.0000




std lib tests:
no valgrind integration
binary size: 9.8M
                  Name       Start         End    Duration     Percent
            Initialize      0.0000      0.0068      0.0068      0.0003
     Semantic Analysis      0.0068      3.0785      3.0716      0.1317
       Code Generation      3.0785      4.3512      1.2727      0.0546
      LLVM Emit Output      4.3512     22.7576     18.4064      0.7895
    Build Dependencies     22.7576     23.0984      0.3408      0.0146
             LLVM Link     23.0984     23.3148      0.2163      0.0093
                 Total      0.0000     23.3148     23.3148      1.0000


valgrind integration
binary size: 11M
                  Name       Start         End    Duration     Percent
            Initialize      0.0000      0.0036      0.0036      0.0001
     Semantic Analysis      0.0036      3.0812      3.0777      0.1264
       Code Generation      3.0812      4.3706      1.2894      0.0530
      LLVM Emit Output      4.3706     23.5837     19.2132      0.7893
    Build Dependencies     23.5837     24.1339      0.5501      0.0226
             LLVM Link     24.1339     24.3428      0.2089      0.0086
                 Total      0.0000     24.3428     24.3428      1.0000

You can see that in practice for debug builds, it makes compile time 4% slower and makes the binary size 11% bigger. Release builds are unchanged, unless you use --enable-valgrind.