LTO compilation flag, also strict compilation warning check

[jangorecki]

follow up of #3864

[codecov]

Codecov Report

Merging #3878 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3878   +/-   ##
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  Coverage   99.42%   99.42%           
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  Files          72       72           
  Lines       13462    13462           
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  Hits        13385    13385           
  Misses         77       77

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[jangorecki]

We need to enable that only for data.table, otherwise there is a failure of installation in other packages. Will submit fix soon.

ar: yajl/yajl.o: plugin needed to handle lto object
ar: yajl/yajl_alloc.o: plugin needed to handle lto object
ar: yajl/yajl_buf.o: plugin needed to handle lto object
ar: yajl/yajl_encode.o: plugin needed to handle lto object
ar: yajl/yajl_gen.o: plugin needed to handle lto object
ar: yajl/yajl_lex.o: plugin needed to handle lto object
ar: yajl/yajl_parser.o: plugin needed to handle lto object
ar: yajl/yajl_tree.o: plugin needed to handle lto object
gcc -std=gnu99 -shared -L/usr/lib/R/lib -Wl,-Bsymbolic-functions -Wl,-z,relro -o jsonlite.so base64.o collapse_array.o collapse_object.o collapse_pretty.o escape_chars.o integer64_to_na.o is_datelist.o is_recordlist.o is_scalarlist.o modp_numtoa.o null_to_na.o num_to_char.o parse.o prettify.o push_parser.o r-base64.o register.o row_collapse.o transpose_list.o validate.o -Lyajl -lstatyajl -L/usr/lib/R/lib -lR
installing to /usr/local/lib/R/site-library/00LOCK-jsonlite/00new/jsonlite/libs
** R
** inst
** byte-compile and prepare package for lazy loading
** help
*** installing help indices
** building package indices
** installing vignettes
** testing if installed package can be loaded from temporary location
Error: package or namespace load failed for ‘jsonlite’ in dyn.load(file, DLLpath = DLLpath, ...):
 unable to load shared object '/usr/local/lib/R/site-library/00LOCK-jsonlite/00new/jsonlite/libs/jsonlite.so':
  /usr/local/lib/R/site-library/00LOCK-jsonlite/00new/jsonlite/libs/jsonlite.so: undefined symbol: yajl_gen_array_close
Error: loading failed