[yocto] cross-compilation of kernel does not work with the generated toolchain?

[Hans Beckérus]

Hi. I am trying to build a kernel using our bitbaked and populated
toolchain. It works fine for user-space application but when trying to
compile the kernel we get

  HOSTCC  scripts/dtc/checks.o
  HOSTCC  scripts/dtc/data.o
  HOSTCC  scripts/dtc/dtc-lexer.lex.o
  HOSTCC  scripts/dtc/dtc-parser.tab.o
  HOSTCC  scripts/dtc/dtc.o
  HOSTCC  scripts/dtc/flattree.o
  HOSTCC  scripts/dtc/fstree.o
  HOSTCC  scripts/dtc/livetree.o
  HOSTCC  scripts/dtc/srcpos.o
In file included from scripts/dtc/dtc.h:25,
                 from scripts/dtc/srcpos.c:24:
/usr/include/string.h:546: error: expected declaration specifiers or
'...' before '__locale_t'
/usr/include/string.h:547: error: nonnull argument with out-of-range
operand number (argument 1, operand 3)
/usr/include/string.h:550: error: expected declaration specifiers or
'...' before '__locale_t'
/usr/include/string.h:551: error: nonnull argument with out-of-range
operand number (argument 1, operand 4)
make[2]: *** [scripts/dtc/srcpos.o] Error 1
make[1]: *** [scripts/dtc] Error 2
make: *** [scripts] Error 2

/usr/include/string.h ??? That must be wrong, or? I expected it to
pickup the standard headerfiles from our toolchain, not the ones on
the build host. That will surely clash with the version of the
compiler being used.

Any ideas what might be wrong here?

Thanks.
Hans