Poor single-threaded allocation performance

[jounathaen]

The current memory allocator seems to have a performance issue:

I've created a test with a 3MiB Json serialization that illustrates the issue:
https://github.com/jounathaen/hermit-allocator-json-test

Allocator	average runtime
host	8.00ms
talc	4748.54ms
bump	28.57ms
galloc	29.98ms

(talc is more than 150x slower than galloc in this scenario)

The alternative allocators are implemented here:

• Memory Allocator: Switch from talc to galloc #1940
• Added simple bump alloc #1935

[jounathaen]

As @m-mueller678 mentioned in #1940 (comment), we (in addition to the current talc problem) might also have a performance penalty from using a single-threaded allocator and a Mutex. This benchmark here is single-threaded if I'm not wrong.