use ctRegex + avoid array allocation

[wilzbach]

These are two simple gotchas that I found during #195 and are independent to it or any refactoring.
Btw interestingly the compilation increases about 0.1s, but for the optimized build it decreases for nearly 0.2s

Compilation

command	compilation time
dmd rdmd-master.d	1.21s
dmd rdmd.d	1.31s
dmd -O rdmd-master.d	1.96s
dmd -O rdmd.d	1.77s

echo rdmd_master.d rdmd.d "-O rdmd" | tr ' ' '\n' | parallel -j1 "echo {}; python -m timeit -n 5 -r 3 -s 'import os' 'os.system(\"dmd {}\")'"

Run time

With the used at #191

command	compilation time
rdmd-master	607ms
rdmd-ct	605ms
rdmd-master-opt	598ms
rdmd-ct-opt	557ms

For a simple file with only two imports

command	compilation time
rdmd-master	135ms
rdmd-ct	133ms
rdmd-master-opt	124ms
rdmd-ct-opt	111ms

For the benchmarks the following command was used :

echo rdmd-master rdmd-ct rdmd-master-opt rdmd-ct-opt | tr ' ' '\n' | parallel -j1 "echo {}; python -m timeit -n 10 -r 3 -s 'import os' 'os.system(\"./{} --force -main t1.d > /dev/null 2>&1\")'"

edit: rdmd-master = commit 1260719

[dlang-bot]

@wilzbach, thanks for your PR! By analyzing the annotation information on this pull request, we identified @andralex, @CyberShadow and @leandro-lucarella-sociomantic to be potential reviewers. @andralex: The PR was automatically assigned to you, please reassign it if you were identified mistakenly.

(The DLang Bot is under development. If you experience any issues, please open an issue at its repo.)

[AndrejMitrovic]

Can we use root.only.chain.myDeps.byKey.anyNewerThan(lastBuildTime) here?

[mihails-strasuns]

IMHO it is much harder to read than current version. I'd even go as far as to say that chain should never be used with UFCS unless it is used to append to already existing pipeline.