Add a SAWscript position to calls to Crucible's malloc

[langston-barrett]

So when users get a Crucible memory dump, they can tell that this allocation was made in a SAW override, rather than in their C/LLVM code.

It would also be good to do this in doAlloc and doAllocConst.

Example (right below Found 1 possibly matching allocation(s)):

Abort due to false assumption:
  All overrides failed during structural matching:
  *  Name: EVP_DigestInit_ex
     Location: /build/fizz-hkdf/digest.saw:198:3
     Argument types: 
     - %struct.env_md_ctx_st*
     - %struct.env_md_st*
     - %struct.engine_st*
     Return type: i32
     at /build/fizz-hkdf/digest.saw:104:3
     error when loading through pointer that appeared in the override's points-to precondition(s):
     Precondition:
       Pointer: concrete pointer: allocation = 645, offset = 72
       Pointee: literal integer: unsigned value = 0, signed value =  0, width = 64
       Assertion made at: /build/fizz-hkdf/digest.saw:104:3
     Failure reason: 
       When reading through pointer (645, 0x48:[64])
       Tried to read something of size: 8
       And type: i64
       Found 1 possibly matching allocation(s):
       - HeapAlloc 645 0x120:[64] Mutable /build/fizz-hkdf/hmac.saw:143:14