[yocto] SDK missing /usr/include/asm header files

[Grant Edwards]

I've built a "poky" SDK for use with a Renesas RZN1 eval board (dual
ARM Cortex-A7 cores), and the toolchain's sysroot seems to be missing
the "asm" header directory.  When I try to compile a simple tcp echo
server program I get this:

    /home/grante/rzn1d/toolchain/sysroots/x86_64-pokysdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-gcc --sysroot=/home/grante/rzn1d/toolchain/sysroots/armv7vehf-vfp-poky-linux-gnueabi -march=armv7ve -marm -mfpu=vfp -mfloat-abi=hard -Wall -Werror -std=gnu99 -c tcpecho.c
    In file included from /home/grante/rzn1d/toolchain/sysroots/armv7vehf-vfp-poky-linux-gnueabi/usr/include/signal.h:287:0,
                 from /home/grante/rzn1d/toolchain/sysroots/armv7vehf-vfp-poky-linux-gnueabi/usr/include/sys/wait.h:36,
                 from tcpecho.c:6:
    /home/grante/rzn1d/toolchain/sysroots/armv7vehf-vfp-poky-linux-gnueabi/usr/include/bits/sigcontext.h:30:11: fatal error: asm/sigcontext.h: No such file or directory
     # include <asm/sigcontext.h>
               ^~~~~~~~~~~~~~~~~~
    compilation terminated.
    make: *** [Makefile:26: tcpecho.o] Error 1

Browsing throught the installed toolchain's sysroot confirms that gcc
is correct: there's no "asm" directory in the sysroot's usr/include
directory (or anywhere else in the toolchain's installation tree).

This is the first time I've tried to build an SDK, so I've probably
done something wrong, but I could use a clue as to what might have
gone wrong...

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