x86/build: Add 'set -e' to mkcapflags.sh to delete broken capflags.c

x86/build: Add 'set -e' to mkcapflags.sh to delete broken capflags.c

Without 'set -e', shell scripts continue running even after any
error occurs. The missed 'set -e' is a typical bug in shell scripting.

For example, when a disk space shortage occurs while this script is
running, it actually ends up with generating a truncated capflags.c.

Yet, mkcapflags.sh continues running and exits with 0. So, the build
system assumes it has succeeded.

It will not be re-generated in the next invocation of Make since its
timestamp is newer than that of any of the source files.

Add 'set -e' so that any error in this script is caught and propagated
to the build system.

Since 9c2af1c7377a ("kbuild: add .DELETE_ON_ERROR special target"),
make automatically deletes the target on any failure. So, the broken
capflags.c will be deleted automatically.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Borislav Petkov <bp@alien8.de>
Link: https://lkml.kernel.org/r/20190625072622.17679-1-yamada.masahiro@socionext.com