perf unwind: Do not overwrite FEATURE_CHECK_LDFLAGS-libunwind-{x86,aarch64}

perf unwind: Do not overwrite FEATURE_CHECK_LDFLAGS-libunwind-{x86,aarch64}

When setting LIBUNWIND_DIR, we first set

 FEATURE_CHECK_LDFLAGS-libunwind-{aarch64,x86} = -L$(LIBUNWIND_DIR)/lib.

<committer note>
This happens a bit before, the overwritting, in:

  libunwind_arch_set_flags = $(eval $(libunwind_arch_set_flags_code))
  define libunwind_arch_set_flags_code
    FEATURE_CHECK_CFLAGS-libunwind-$(1)  = -I$(LIBUNWIND_DIR)/include
    FEATURE_CHECK_LDFLAGS-libunwind-$(1) = -L$(LIBUNWIND_DIR)/lib
  endef

  ifdef LIBUNWIND_DIR
    LIBUNWIND_CFLAGS  = -I$(LIBUNWIND_DIR)/include
    LIBUNWIND_LDFLAGS = -L$(LIBUNWIND_DIR)/lib
    LIBUNWIND_ARCHS = x86 x86_64 arm aarch64 debug-frame-arm debug-frame-aarch64
    $(foreach libunwind_arch,$(LIBUNWIND_ARCHS),$(call libunwind_arch_set_flags,$(libunwind_arch)))
  endif

Look at that 'foreach' on all the LIBUNWIND_ARCHS.
</>

After commit 5c4d7c82c0dc ("perf unwind: Do not put libunwind-{x86,aarch64}
in FEATURE_TESTS_BASIC"), FEATURE_CHECK_LDFLAGS-libunwind-{x86,aarch64} is
overwritten. As a result, the remote libunwind libraries cannot be searched
from $(LIBUNWIND_DIR)/lib directory during feature check tests. Fix it with
variable appending.

Before this patch:

  perf$ make VF=1 LIBUNWIND_DIR=/opt/libunwind_aarch64
   BUILD:   Doing 'make -j16' parallel build
  <SNIP>
  ...
  ...                    libopencsd: [ OFF ]
  ...                 libunwind-x86: [ OFF ]
  ...              libunwind-x86_64: [ OFF ]
  ...                 libunwind-arm: [ OFF ]
  ...             libunwind-aarch64: [ OFF ]
  ...         libunwind-debug-frame: [ OFF ]
  ...     libunwind-debug-frame-arm: [ OFF ]
  ... libunwind-debug-frame-aarch64: [ OFF ]
  ...                           cxx: [ OFF ]
  <SNIP>

  perf$ cat ../build/feature/test-libunwind-aarch64.make.output
  /usr/bin/ld: cannot find -lunwind-aarch64
  /usr/bin/ld: cannot find -lunwind-aarch64
  collect2: error: ld returned 1 exit status

After this patch:

  perf$ make VF=1 LIBUNWIND_DIR=/opt/libunwind_aarch64
   BUILD:   Doing 'make -j16' parallel build
  <SNIP>
  ...                    libopencsd: [ OFF ]
  ...                 libunwind-x86: [ OFF ]
  ...              libunwind-x86_64: [ OFF ]
  ...                 libunwind-arm: [ OFF ]
  ...             libunwind-aarch64: [ on  ]
  ...         libunwind-debug-frame: [ OFF ]
  ...     libunwind-debug-frame-arm: [ OFF ]
  ... libunwind-debug-frame-aarch64: [ OFF ]
  ...                           cxx: [ OFF ]
  <SNIP>

  perf$ cat ../build/feature/test-libunwind-aarch64.make.output

  perf$ ldd ./perf
        linux-vdso.so.1 (0x00007ffdf07da000)
        libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f30953dc000)
        librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007f30951d4000)
        libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f3094e36000)
        libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f3094c32000)
        libelf.so.1 => /usr/lib/x86_64-linux-gnu/libelf.so.1 (0x00007f3094a18000)
        libdw.so.1 => /usr/lib/x86_64-linux-gnu/libdw.so.1 (0x00007f30947cc000)
        libunwind-x86_64.so.8 => /usr/lib/x86_64-linux-gnu/libunwind-x86_64.so.8 (0x00007f30945ad000)
        libunwind.so.8 => /usr/lib/x86_64-linux-gnu/libunwind.so.8 (0x00007f3094392000)
        liblzma.so.5 => /lib/x86_64-linux-gnu/liblzma.so.5 (0x00007f309416c000)
        libunwind-aarch64.so.8 => not found
        libslang.so.2 => /lib/x86_64-linux-gnu/libslang.so.2 (0x00007f3093c8a000)
        libpython2.7.so.1.0 => /usr/local/lib/libpython2.7.so.1.0 (0x00007f309386b000)
        libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f309364e000)
        libnuma.so.1 => /usr/lib/x86_64-linux-gnu/libnuma.so.1 (0x00007f3093443000)
        libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f3093052000)
        /lib64/ld-linux-x86-64.so.2 (0x00007f3096097000)
        libbz2.so.1.0 => /lib/x86_64-linux-gnu/libbz2.so.1.0 (0x00007f3092e42000)
        libutil.so.1 => /lib/x86_64-linux-gnu/libutil.so.1 (0x00007f3092c3f000)

Fixes: 5c4d7c82c0dceccf ("perf unwind: Do not put libunwind-{x86,aarch64} in FEATURE_TESTS_BASIC")
Signed-off-by: Li Huafei <lihuafei1@huawei.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Zhang Jinhao <zhangjinhao2@huawei.com>
Link: http://lore.kernel.org/lkml/20210823134340.60955-1-lihuafei1@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>