fix(lambda-layer): drop unused libicu DT_NEEDED via --as-needed linker flag

AL2023's boost-devel puts libicu on the linker's library path. The default
ld behaviour records every library in scope as DT_NEEDED, so libparquet.so
ended up declaring libicudata/libicui18n/libicuuc as runtime deps even
though Arrow uses zero ICU symbols (confirmed by `objdump -T`). Lambda's
AL2023 runtime doesn't ship libicu, so layers for py3.12+ failed to
import with "libicudata.so.67: cannot open shared object file".

Pass -Wl,--as-needed via CMAKE_{SHARED,EXE}_LINKER_FLAGS so the linker
omits DT_NEEDED entries for libraries whose symbols are never referenced.
This is the proper fix for the original problem PR #3336 worked around —
it now applies generally rather than relying on libicu being absent from
the build env.

Author: kukushking

building/lambda/build-lambda-layer.sh

@@ -26,9 +26,16 @@ mkdir $ARROW_HOME
 mkdir arrow/cpp/build
 pushd arrow/cpp/build
 
+# -Wl,--as-needed drops DT_NEEDED entries for libraries whose symbols are never
+# referenced. On AL2023, boost-devel pulls libicu into the linker's library
+# path; without --as-needed, libparquet.so picks up libicudata/libicui18n/
+# libicuuc as DT_NEEDED even though Arrow uses zero ICU symbols. Lambda's
+# AL2023 runtime doesn't ship libicu, so the resulting layer fails to import.
 cmake \
     -DCMAKE_INSTALL_PREFIX=$ARROW_HOME \
     -DCMAKE_INSTALL_LIBDIR=lib \
+    -DCMAKE_SHARED_LINKER_FLAGS="-Wl,--as-needed" \
+    -DCMAKE_EXE_LINKER_FLAGS="-Wl,--as-needed" \
     -DARROW_PYTHON=ON \
     -DARROW_PARQUET=ON \
     -DARROW_DATASET=ON \