Support asm/disasm on Windows

[peace-maker]

Find binutils toolchains like https://gnutoolchains.com/ if they exist in the PATH. This allows to assemble and disassemble shellcode natively on Windows using pwntools.

PS C:\> asm -c amd64 "mov rax, 5"
48c7c005000000
PS C:\> disasm -c amd64 48c7c005000000
   0:    48 c7 c0 05 00 00 00     mov    rax,  0x5
PS C:\> shellcraft amd64.windows.cmd
[!] Could not find system include headers for amd64-windows
31f665488b5e60488b5b18488b732048ad489648ad488b5820448b433c4c89c24801da4531c941b1884c01ca448b024901d8418b70204801de4831c949b947657450726f634148ffc18b048e4801d84c390875f2418b70244801de668b0c4e418b701c4801de8b048e4801d84889c748b801010101010101015048b856686f4479646201483104244889e231f665488b4e60488b4918488b712048ad489648ad488b48204883ec30ffd74883c4384889c648b801010101010101015048b8626c652f64796401483104244889e14883ec3031d2ffd64883c438ebfe