Compilation syntax issue on package install about modelmetrics HOT 4 CLOSED

sessionInfo()
R version 3.5.1 (2018-07-02)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Antergos Linux

Matrix products: default
BLAS/LAPACK: /opt/intel/compilers_and_libraries_2018.1.163/linux/mkl/lib/intel64_lin/libmkl_gf_lp64.so

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
 [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
 [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
 [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

loaded via a namespace (and not attached):
 [1] Rcpp_0.12.19         compiler_3.5.1       prettyunits_1.0.2   
 [4] base64enc_0.1-3      remotes_2.0.2        tools_3.5.1         
 [7] testthat_2.0.1       digest_0.6.18        pkgbuild_1.0.2.9000 
[10] pkgload_1.0.2        bit_1.1-14           memoise_1.1.0       
[13] RSQLite_2.1.1        debugme_1.1.0        pkgconfig_2.0.2     
[16] rlang_0.3.0.9000     cli_1.0.1.9000       DBI_1.0.0           
[19] curl_3.2             withr_2.1.2          desc_1.2.0          
[22] fs_1.2.6             devtools_2.0.1       rappdirs_0.3.1      
[25] rprojroot_1.3-2      bit64_0.9-7          glue_1.3.0          
[28] crancache_0.0.0.9000 parsedate_1.1.3      R6_2.3.0            
[31] processx_3.2.0.9000  tcltk_3.5.1          sessioninfo_1.1.0   
[34] callr_3.0.0.9001     blob_1.1.1           magrittr_1.5        
[37] backports_1.1.2      ps_1.2.0             usethis_1.4.0       
[40] assertthat_0.2.0     cranlike_1.0.1.9001  crayon_1.3.4