I'm seeing similar error messages when trying to install the readxl and dplyr packages in R 3.6.3 om Mac Mojave.
install.packages("readxl", type = "source")
In file included from /Users/sm*****et/Library/R/3.6/library/progress/include/RProgress.h:6:
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/unistd.h:732:31: error: unknown type name 'uuid_t'; did you mean 'uid_t'?
int setwgroups_np(int, const uuid_t);
install.packages("dplyr", type = "source")
In file included from /Users/sm***et/Library/R/3.6/library/BH/include/boost/config/detail/posix_features.hpp:18:
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/unistd.h:732:31: error: unknown type name 'uuid_t'; did you mean 'uid_t'?
int setwgroups_np(int, const uuid_t);