kbuild: pass LDFLAGS to recordmcount.pl

Since commit 0fbe9a24 ("microblaze: add endianness options to
LDFLAGS instead of LD"), you cannot build the kernel for microblaze
with CONFIG_DYNAMIC_FTRACE.

Fixes: 0fbe9a24

 ("microblaze: add endianness options to LDFLAGS instead of LD")
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>