package/coremark-pro: fix build with uclibc-ng

package/coremark-pro: fix build with uclibc-ng

Fix the following linking error with uClibc-ng:

/nvme/rc-buildroot-test/scripts/instance-1/output-1/host/bin/arc-buildroot-linux-uclibc-gcc  -o/nvme/rc-buildroot-test/scripts/instance-1/output-1/build/coremark-pro-1.1.2743/builds/linux/gcc/bin/cjpeg-rose7-preset cjpeg-rose7-preset.o /nvme/rc-buildroot-test/scripts/instance-1/output-1/build/coremark-pro-1.1.2743/builds/linux/gcc/obj/bench/consumer_v2/cjpeg/*.o  /nvme/rc-buildroot-test/scripts/instance-1/output-1/build/coremark-pro-1.1.2743/builds/linux/gcc/obj/mith.a -lm -lpthread  -lrt
/nvme/rc-buildroot-test/scripts/instance-1/output-1/host/lib/gcc/arc-buildroot-linux-uclibc/10.2.0/../../../../arc-buildroot-linux-uclibc/bin/ld: /nvme/rc-buildroot-test/scripts/instance-1/output-1/host/lib/gcc/arc-buildroot-linux-uclibc/10.2.0/libgcc.a(unwind-dw2-fde-dip.o): in function `_Unwind_Find_FDE':
/nvme/rc-buildroot-test/scripts/instance-1/output-1/build/host-gcc-final-arc-2020.09-release/build/arc-buildroot-linux-uclibc/libgcc/../../../libgcc/unwind-dw2-fde-dip.c:469: undefined reference to `dl_iterate_phdr'
/nvme/rc-buildroot-test/scripts/instance-1/output-1/host/lib/gcc/arc-buildroot-linux-uclibc/10.2.0/../../../../arc-buildroot-linux-uclibc/bin/ld: /nvme/rc-buildroot-test/scripts/instance-1/output-1/build/host-gcc-final-arc-2020.09-release/build/arc-buildroot-linux-uclibc/libgcc/../../../libgcc/unwind-dw2-fde-dip.c:469: undefined reference to `dl_iterate_phdr'
/nvme/rc-buildroot-test/scripts/instance-1/output-1/host/lib/gcc/arc-buildroot-linux-uclibc/10.2.0/../../../../arc-buildroot-linux-uclibc/bin/ld: GOT and PLT relocations cannot be fixed with a non dynamic linker
/nvme/rc-buildroot-test/scripts/instance-1/output-1/host/lib/gcc/arc-buildroot-linux-uclibc/10.2.0/../../../../arc-buildroot-linux-uclibc/bin/ld: final link failed: bad value
collect2: error: ld returned 1 exit status
/nvme/rc-buildroot-test/scripts/instance-1/output-1/build/coremark-pro-1.1.2743/workloads/cjpeg-rose7-preset//Makefile:65: recipe for target '/nvme/rc-buildroot-test/scripts/instance-1/output-1/build/coremark-pro-1.1.2743/builds/linux/gcc/bin/cjpeg-rose7-preset' failed

Since uClibc-ng 1.0.18 a circular dependency between libc and libgcc
exist, when static linking is used. It can be resolved by the compiler
when -static is correctly passed in the linking step.

So use TARGET_LDFLAGS to pass LDFLAGS

Fixes:
 - http://autobuild.buildroot.org/results/ca86624b09fed961d2b9086fee8b2029845746ea

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>