Several minor issues collection for section_1

[Atcold]

I've encountered several issues when going over the first few chapters of your book.

• There are no instructions on how to compile .cpp files (the book mentions clang but clang++ needs to be used instead).
• Many code assembly blocks start with ```text instead of ```asm.
• section_1/hello_world/v3.cpp -> section_1/hello_world/v3.c.
• section_1/if doesn't have a macOS version (section_1/hello_world introduces macros that here are not used).
• v6.S uses PUSH_P and PUSH_R, which are not explained. Maybe for pushing a Pair of registers or a single Register to the stack.
• v6.S moves sp to x29 for no clear reason.
• v6.S uses 1: and 2: labels and 2f and 1b, which are only explained in a later chapter.
• hello_world/README.md says that for (; argv; argv++) has the "added benefit that the increment of the argv pointer is not a side effect" which is not true. After the loop, argv value is no longer the initial one.
• xzr in mov x0, xzr in section_1/hello_world/v5.s has never been defined (and it's less readable than mov x0, #0).
• section_1/structs/alignment.md talks about a hex dump, but there are no instructions about how to do such a thing. So, it's impossible to follow along what the book is explaining.
• I don't know how to compile section_1/structs/test01.c for inspecting the binary.

I didn't want to create a separate issue for each item.
I hope you do appreciate this kind of feedback.

P.S. I've pushed some of these changes to my fork of your repo.

[Atcold]

Addressing the alignment issue here.

To compile section_1/structs/test01.c use clang -c test01.c on Mac or gcc -c test01.c on Linux.
To hex dump it, use xxd test01.o.

The relevant part is reproduced below.

00000180: 0000 0000 0000 0000 aaaa aaaa aaaa aaaa  ................
00000190: bbbb 0000 cccc cccc 1100 ffee ddcc bbaa  ................
000001a0: 3322 0000 7766 5544 1100 0000 0e01 0000  3"..wfUD........

The source code is the following.

struct Foo {
    long a;
    short b;
    int c;
};

struct Foo Bar = { 0xaaaaaaaaaaaaaaaa, 0xbbbb, 0xcccccccc };
struct Foo Fee = { 0xaabbccddeeff0011, 0x2233, 0x44556677 };

Notice how 0xaabbccddeeff0011 is stored in memory as 1100 ffee ddcc bbaa (little endian format).