libc: handle sync_file_range

Add cancellation and support arm, ppc64, mips32.
Compile-tested.

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
arm: workaround GCC PR target/53735 with fork()

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
buildsys: prevent make from searching for .config

Fixes:
make distclean
mkdir /.config
make -C test/API clean
Reading makefile `../../.config' (search path) (don't care) (no ~ expansion)...
make: *** ../../.config: Is a directory.  Stop.

write(1, "Reading makefile `../../.config'"..., 80) = 80
open("../../.config", O_RDONLY)         = -1 ENOENT (No such file or directory)
open("/usr/include/../../.config", O_RDONLY) = 6
fstat(6, {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
read(6, 0x7f2fe3bfc000, 4096)           = -1 EISDIR (Is a directory)

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
dl: fix dlsym lookups with RTLD_NEXT

The current code for dlsym() when invoked with RTLD_NEXT lookup
searches for the module where it's being called from, and executes the
_dl_find_hash only for the next module in the chain. However, if the
looked symbol is not there, the rest of the modules are not checked.

Generally this is not a problem as symbols are merged for the parent
modules; so this affects only RTLD_NEXT.

This patch adds a loop iterating through all the following modules.

Signed-off-by: Timo Teräs <timo.teras@iki.fi>
Reviewed-by: Filippo ARCIDIACONO <filippo.arcidiacono@st.com>
Tested-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
libc: add {get,set,swap,make}context user context manipulation functions

Add the obsolescent SUSv3 family of user context manipulating functions
for arm, i386, mips, x86_64.

Signed-off-by: Timon ter Braak <timonterbraak@gmail.com>
Signed-off-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
Signed-off-by: Natanael Copa <ncopa@alpinelinux.org>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
buildsys: remove superfluous default n

kconfig's default defaults to n so spelling out default n is redundant

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
buildsys: use kbuild style

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>