[bfd][arm] Don't assert on suspicious build attributes in input file

[bfd][arm] Don't assert on suspicious build attributes in input file

It's generally a bad idea to use assertions to validate our idea of
what an input file looks like.  We need to be as liberal as possible
in what we accept with respect to standards and conservative with what
we produce.

Currently, if gcc is used to produce an assembler file which contains
only data, but the FPU is set to fpv4-sp-d16 and mfloat-abi=hard, then
the following attributes will be set in the output:

        .cpu arm7tdmi
        .eabi_attribute 27, 1   @ Tag_ABI_HardFP_use
        .eabi_attribute 28, 1   @ Tag_ABI_VFP_args
        .eabi_attribute 20, 1   @ Tag_ABI_FP_denormal
        .eabi_attribute 21, 1   @ Tag_ABI_FP_exceptions
        .eabi_attribute 23, 3   @ Tag_ABI_FP_number_model
        .eabi_attribute 24, 1   @ Tag_ABI_align8_needed
        .eabi_attribute 25, 1   @ Tag_ABI_align8_preserved
        .eabi_attribute 26, 2   @ Tag_ABI_enum_size
        .eabi_attribute 30, 6   @ Tag_ABI_optimization_goals
        .eabi_attribute 34, 0   @ Tag_CPU_unaligned_access
        .eabi_attribute 18, 4   @ Tag_ABI_PCS_wchar_t

There is then no .fpu directive to cause Tag_FP_arch to be set,
because there are no functions containing code in the object file.  If
this object file is assembled by hand, but without -mfpu on the
invocation of the assembler, then the build attributes produced will
trigger an assertion during linking.

Thinking about the build attributes, the combination of a
single-precision only implementation of no floating-point architecture
is still no floating-point architecture.  Hence the assertion on the
input BFD in the linker makes no real sense.

We should, however, be more conservative in what we generate, so I've
left the assertion on the output bfd in place; I don't think we can
trigger it with this change since we never merge the problematic tags
from a perversely generated input file.

	* elf32-arm.c (elf32_arm_merge_eabi_attributes): Remove assertion
	that the input bfd has Tag_FP_ARCH non-zero if Tag_ABI_HardFP_use
	is non-zero.  Add clarifying comments.