posix: don't rely on undefined behavior of signed integer overflow

[marcinslusarz]

Fixes issue reported by ASAN: src/libpmemfile-posix/lseek.c:283:39: runtime error: signed integer overflow: 3 + 9223372036854775807 cannot be represented in type 'long' SUMMARY: AddressSanitizer: undefined-behavior /src/libpmemfile-posix/lseek.c:283:39 in src/libpmemfile-posix/lseek.c:294:39: runtime error: signed integer overflow: 9 + 9223372036854775806 cannot be represented in type 'long' SUMMARY: AddressSanitizer: undefined-behavior src/libpmemfile-posix/lseek.c:294:39 in

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This change is 

[krzycz]

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Reviewed 1 of 1 files at r1. Review status: all files reviewed at latest revision, all discussions resolved.

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Comments from Reviewable

[codecov-io]

Codecov Report

Merging #321 into master will increase coverage by 0.05%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #321      +/-   ##
==========================================
+ Coverage    77.5%   77.55%   +0.05%     
==========================================
  Files          90       90              
  Lines       13811    13816       +5     
  Branches     1994     1995       +1     
==========================================
+ Hits        10704    10715      +11     
+ Misses       2383     2381       -2     
+ Partials      724      720       -4

Impacted Files	Coverage Δ
src/libpmemfile-posix/lseek.c	89.79% <100%> (+0.28%)	:arrow_up:
tests/posix/mt/mt.cpp	85.41% <0%> (-1.05%)	:arrow_down:
src/libpmemfile-posix/file.c	66.85% <0%> (+0.09%)	:arrow_up:
src/libpmemfile-posix/dir.c	82.06% <0%> (+0.24%)	:arrow_up:
src/libpmemfile-posix/utils.c	73.43% <0%> (+0.42%)	:arrow_up:
src/libpmemfile-posix/rename.c	91.93% <0%> (+1.2%)	:arrow_up:
src/libpmemfile-posix/read.c	91.83% <0%> (+1.49%)	:arrow_up:
src/libpmemfile/syscall_early_filter.c	80% <0%> (+20%)	:arrow_up:

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[sarahjelinek]

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Review status: :shipit: all files reviewed at latest revision, all discussions resolved, all commit checks successful.

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Comments from Reviewable

[GBuella]

Well, that cast is implementation defined instead of undefined, but I guess UBSAN and ASAN only look for UB. Anyway, it would have been cleaner to not rely on implementation either.