time64.inc: Simplify GLIBC_64BIT_TIME_FLAGS usage

time64.inc: Simplify GLIBC_64BIT_TIME_FLAGS usage

The implementation uses the append operator to include
GLIBC_64BIT_TIME_FLAGS in TARGET_CC_ARCH, but it places the space in
the GLIBC_64BIT_TIME_FLAGS assignment in order to avoid a 'spurious
space' when the value is empty.

68b50d3 time64: Remove leading whitespace from GLIBC_64BIT_TIME_FLAGS

The problem with this is it requires anyone wishing to assign a value
to GLIBC_64BIT_TIME_FLAGS to add the leading space, otherwise this is
the error:

cc1: error: '-Werror=format-security-D_TIME_BITS=64': no option '-Wformat-security-D_TIME_BITS=64'

Add a new constant variable to capture the value needed for the 32-bit
special case, including the space.

Signed-off-by: Tom Hochstein <tom.hochstein@oss.nxp.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>