Can't get Linux libraries during cross-compilation

Hi everybody
In my project I use a plugin that, based on the target platform/compiler, consider different libraries. When cross-compiling for Linux, the plugin considers a GNU library that I can easly found in my Linux toolchain at the following path:“C:\Linux_CrossCompileToolChain\x86_64-unknown-linux-gnu\usr\include”,but it seems that it’s ignored.
More specifically the library is “byteswap.h”. What am I doing wrong? Should I have to set some definition in the plugin’s *.Build.cs?