1. Move exepath_*() related code to libc/misc
1. Rename exepath_ to envpath_
2. Rename BINFMT_EXEPATH to LIB_ENVPATH
libs/libc/modlib: Add pre module library symbol table support
binfmt/, libs/libc/unistd, and others: Rename CONFIG_EXECFUNCS_SYMTAB to CONFIG_EXECFUNCS_SYMTAB_ARRAY. Rename CONFIG_EXECFUNCS_NSYMBOLS to CONFIG_EXECFUNCS_NSYMBOLS_VAR. Unlike CONFIG_EXECFUNCS_NSYMBOLS, CONFIG_EXECFUNCS_NSYMBOLS_VAR holds the name of an 'int' variable that contains the number of symbols in the symbol table.
configs/sama5d4-ek: Partial update to knsh build instructions.
Squashed commit of the following:
libs/libxx: Fix some confusing in naming. If the directory is called libxx, then the library must be libxx.a (unless perhaps LIBCXX is selected).
libs/: Fix paths in moved library directories.
libs: Brute force move of libc, libnx, and libxx to libs. Cannot yet build it in that configuration.
