Fix breaking change in builtin casts functions

[lorrding]

While healing with Eowyn I noticed that two exercises are broken on latest build to date (0.11.0-dev.3747).

I looked up the doc and it seems that builtin casts functions changed name in a very recent build.

So instead of the old @enumToInt and @intToFloat we need to use @intFromEnum and @floatFromInt

This affects 036_enums2.zig and 096_memory_allocation.zig

Before breaking change:

ubuntu@temp:~/ziglings$ zig version
0.11.0-dev.3395+7b5bd3a93
ubuntu@temp:~/ziglings$ zig build -Dhealed -Dn=36
         _       _ _
     ___(_) __ _| (_)_ __   __ _ ___
    |_  | |/ _' | | | '_ \ / _' / __|
     / /| | (_| | | | | | | (_| \__ \
    /___|_|\__, |_|_|_| |_|\__, |___/
           |___/           |___/

    "Look out! Broken programs below!"

Compiling 036_enums2.zig...
Checking 036_enums2.zig...
PASSED:
<p>
  <span style="color: #ff0000">Red</span>
  <span style="color: #00ff00">Green</span>
  <span style="color: #0000ff">Blue</span>
</p>

Before fix:

ubuntu@temp:~/ziglings$ zig version
0.11.0-dev.3747+7b5bd3a93
ubuntu@temp:~/ziglings$ zig build -Dhealed -Dn=36
         _       _ _
     ___(_) __ _| (_)_ __   __ _ ___
    |_  | |/ _' | | | '_ \ / _' / __|
     / /| | (_| | | | | | | (_| \__ \
    /___|_|\__, |_|_|_| |_|\__, |___/
           |___/           |___/

    "Look out! Broken programs below!"

Compiling 036_enums2.zig...
error: the following command failed with 1 compilation errors:
/usr/bin/zig/zig build-exe /home/ubuntu/ziglings/exercises/036_enums2.zig --cache-dir /home/ubuntu/ziglings/zig-cache --listen=- 
exercises/036_enums2.zig:60:9: error: invalid builtin function: '@enumToInt'
        @enumToInt(Color.red),
        ^~~~~~~~~~~~~~~~~~~~~

Ziglings hint: I'm feeling blue about this.
Edit exercises/036_enums2.zig and run 'zig build -Dn=36' again.

After fix:

ubuntu@temp:~/ziglings$ zig version
0.11.0-dev.3747+7b5bd3a93
ubuntu@temp:~/ziglings$ zig build -Dhealed -Dn=36
         _       _ _
     ___(_) __ _| (_)_ __   __ _ ___
    |_  | |/ _' | | | '_ \ / _' / __|
     / /| | (_| | | | | | | (_| \__ \
    /___|_|\__, |_|_|_| |_|\__, |___/
           |___/           |___/

    "Look out! Broken programs below!"

Compiling 036_enums2.zig...
Checking 036_enums2.zig...
PASSED:
<p>
  <span style="color: #ff0000">Red</span>
  <span style="color: #00ff00">Green</span>
  <span style="color: #0000ff">Blue</span>
</p>

I hope I did everything right, I'm new to the repo and zig, so feel free to point out anything wrong

[chrboesch]

Thank you!

[lorrding]

@chrboesch
I forgot to check for comments!

There's some comments especially in 065_builtins2.zig that are now outdated:

ziglings/exercises/065_builtins2.zig

Lines 7 to 10 in 08e8a0f

	// ...and lots of type casting operations such as...
	//
	// @as @intToError @intToFloat
	// @intToPtr @ptrToInt @enumToInt

I updated my branch, but you were quicker that I expected 😅 Do I need to make another PR ?
We need to update 036_enums2, 064_builtins and 065_builtins2

[chrboesch]

Do I need to make another PR ?

Everything works fine! 😄