C++ toolchain support

[stephenrkell]

Conceptually, very little is missing for us to introspect on C++. But one unfortunate thing is that dumpallocs.ml does not work on C++ source, so we will need a C++ified version of that anyway... there is at least one C++ clang-based tool in toolsub that would be a good base.

Continuing that thought: if it uses (built-in) operator new then we need to add this to our list of allocation functions. The binary analysis (objdumpallocs / objdumpmeta) should have no trouble with this. At source level, the built-in operator new is polymorphic, but at linker level it always seems to come out as operator new[](unsigned long). If I write a simple bit of C++ code that does new...

$ diff -u <( objdump -rd test.o ) <( objdump -rd test.o| c++filt )
--- /dev/fd/63  2024-03-06 11:14:14.893088042 +0000
+++ /dev/fd/62  2024-03-06 11:14:14.893088042 +0000
@@ -10,40 +10,40 @@
    4:  48 83 ec 10             sub    $0x10,%rsp
    8:  bf a8 00 00 00          mov    $0xa8,%edi
    d:  e8 00 00 00 00          callq  12 <main+0x12>
-                       e: R_X86_64_PLT32       _Znam-0x4
+                       e: R_X86_64_PLT32       operator new[](unsigned long)-0x4
   12:  48 89 45 f8             mov    %rax,-0x8(%rbp)
   16:  be 2a 00 00 00          mov    $0x2a,%esi
   1b:  48 8d 3d 00 00 00 00    lea    0x0(%rip),%rdi        # 22 <main+0x22>
                        1e: R_X86_64_PC32       e+0xc
...

So in our C++ified version ofdumpallocs.ml, as well as doing the sizeofness analysis for C-style allocation functions (or maybe the generalised version of it mooted in #63), we need something simpler for C++ that can dump the source type of a built-in operator new application.