configure: arm: Don't try to enable pic for shared libraries on win32

The object file format doesn't support PIC loads in ARM assembly,
there are no relocation types in PE/COFF that correspond to
BFD_RELOC_32_PCREL (R_ARM_REL32 in ELF).

Signed-off-by: Martin Storsjö <martin@martin.st>
configure: Don't explicitly disable PIC for windows targets

This reverts e08c946c6 and 05165c2f7a. The actual intention of
e08c946c6 was to fix shared library builds for arm/win32, which
can also be accomplished in other ways.

Disabling pic on those platforms broke inline assembly on cygwin/64
(since some inline assembly requires knowing whether we are building
as PIC or not), and might also break inline assembly on other
compilers on windows.

As a side-effect, this unfortunately brings back all the warnings
about PIC not having any effect on that platform.

Signed-off-by: Martin Storsjö <martin@martin.st>
configure: Don't add -fPIC on windows targets

This avoids warnings about this option not having any effect on
this platform.

We still want to enable the pic configure item for these platforms
(if detected via the compiler builtin define __PIC__) to get proper
inline assembly workarounds.

Signed-off-by: Martin Storsjö <martin@martin.st>