Fix build issues on OSX 10.12

[superfell]

I ran into some issues building on OSX 10.12 with AppleClang 9.0.0.9000039, which this PR addresses.

/Users/sfell/code/zindex/src/Pipe.cpp:10:41: error: no member named 'to_string' in namespace 'std'
                                 + std::to_string(errno)); // TODO: errno
                                   ~~~~~^
/Users/sfell/code/zindex/src/Pipe.cpp:10:51: error: use of undeclared identifier 'errno'
                                 + std::to_string(errno)); // TODO: errno
/Users/sfell/code/zindex/src/RegExpIndexer.h:12:5: error: unknown type name 'uint'; did you mean 'int'?
    uint captureGroup_;
    ^~~~
    int

[codecov[bot]]

Codecov Report

Merging #34 into master will increase coverage by 3.17%. The diff coverage is n/a.

@@            Coverage Diff            @@
##           master     #34      +/-   ##
=========================================
+ Coverage   51.62%   54.8%   +3.17%     
=========================================
  Files          40      40              
  Lines        4982    5020      +38     
  Branches      540       0     -540     
=========================================
+ Hits         2572    2751     +179     
- Misses       2229    2269      +40     
+ Partials      181       0     -181

Impacted Files	Coverage Δ
src/Pipe.cpp	50% <ø> (+10.71%)	:arrow_up:
src/RegExpIndexer.h	100% <ø> (ø)	:arrow_up:
src/Log.h	68.18% <0%> (-3.25%)	:arrow_down:
tests/IndexTest.cpp	99.25% <0%> (+0.74%)	:arrow_up:
tests/catch.hpp	37.33% <0%> (+2.72%)	:arrow_up:
src/LineFinder.cpp	100% <0%> (+3.03%)	:arrow_up:
src/Sqlite.cpp	95.23% <0%> (+3.57%)	:arrow_up:
tests/SqliteTest.cpp	100% <0%> (+4.76%)	:arrow_up:
src/RegExp.cpp	82.92% <0%> (+4.87%)	:arrow_up:
src/RegExpIndexer.cpp	92.3% <0%> (+7.69%)	:arrow_up:
... and 6 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update a74fb63...97743dd. Read the comment docs.

[mattgodbolt]

Good spot! Thanks so much for this fix!