busybox

arch/{sparc,sparc64}/Makefile: define ARCH_FPIC

Building Busybox on SPARC or SPARC64 with CONFIG_BUILD_LIBBUSYBOX=y
currently fails with:

miscutils/lib.a(i2c_tools.o): In function `i2c_dev_open':
i2c_tools.c:(.text.i2c_dev_open+0x14): relocation truncated to fit: R_SPARC_GOT13 against `.LC0'
i2c_tools.c:(.text.i2c_dev_open+0x38): relocation truncated to fit: R_SPARC_GOT13 against symbol `bb_errno' defined in COMMON section in libbb/lib.a(ptr_to_globals.o)
i2c_tools.c:(.text.i2c_dev_open+0x6c): relocation truncated to fit: R_SPARC_GOT13 against `.LC1'
miscutils/lib.a(i2c_tools.o): In function `check_funcs_test_end':
i2c_tools.c:(.text.check_funcs_test_end+0x24): relocation truncated to fit: R_SPARC_GOT13 against `.LC2'
i2c_tools.c:(.text.check_funcs_test_end+0x2c): relocation truncated to fit: R_SPARC_GOT13 against `.LC3'
miscutils/lib.a(i2c_tools.o): In function `check_read_funcs':
i2c_tools.c:(.text.check_read_funcs+0x30): relocation truncated to fit: R_SPARC_GOT13 against `.LC10'
i2c_tools.c:(.text.check_read_funcs+0x80): relocation truncated to fit: R_SPARC_GOT13 against `.LC4'
i2c_tools.c:(.text.check_read_funcs+0x98): relocation truncated to fit: R_SPARC_GOT13 against `.LC5'
i2c_tools.c:(.text.check_read_funcs+0xc0): relocation truncated to fit: R_SPARC_GOT13 against `.LC6'
i2c_tools.c:(.text.check_read_funcs+0xe0): relocation truncated to fit: R_SPARC_GOT13 against `.LC7'
i2c_tools.c:(.text.check_read_funcs+0xf8): additional relocation overflows omitted from the output

As stated by the gcc documentation, the SPARC architecture has a
limited GOT size, which prevents moderately large binaries to be built
with -fpic, and -fPIC is necessary. From gcc's documentation:

'-fpic'
     Generate position-independent code (PIC) suitable for use in a
     shared library, if supported for the target machine.  Such code
     accesses all constant addresses through a global offset table
     (GOT).  The dynamic loader resolves the GOT entries when the
     program starts (the dynamic loader is not part of GCC; it is part
     of the operating system).  If the GOT size for the linked
     executable exceeds a machine-specific maximum size, you get an
     error message from the linker indicating that '-fpic' does not
     work; in that case, recompile with '-fPIC' instead.  (These
     maximums are 8k on the SPARC, 28k on AArch64 and 32k on the m68k
     and RS/6000.  The x86 has no such limit.)

'-fPIC'
     If supported for the target machine, emit position-independent
     code, suitable for dynamic linking and avoiding any limit on the
     size of the global offset table.  This option makes a difference on
     AArch64, m68k, PowerPC and SPARC.

With a limit of 8KB on SPARC, we quickly reach this limit, and we hit
it when building Busybox on SPARC/SPARC64 with the
CONFIG_BUILD_LIBBUSYBOX=y option enabled.

Therefore, this commit redefines ARCH_FPIC as -fPIC on sparc and
sparc64 to solve this issue.

[Submitted upstream: http://lists.busybox.net/pipermail/busybox/2017-July/085633.html]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>