[LLDB][doc] Updates build instructions. (#84630)

Recently building libc++ requires building libunwind too. This updates
the LLDB instructions.

I noticed this recently and it was separately filed as
#84053

Author: mordante

lldb/docs/resources/build.rst

@@ -331,7 +331,7 @@ macOS
 ^^^^^
 
 On macOS the LLDB test suite requires libc++. Either add
-``LLVM_ENABLE_RUNTIMES="libcxx;libcxxabi"`` or disable the test suite with
+``LLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind"`` or disable the test suite with
 ``LLDB_INCLUDE_TESTS=OFF``. Further useful options:
 
 * ``LLDB_BUILD_FRAMEWORK:BOOL``: Builds the LLDB.framework.
@@ -370,7 +370,7 @@ LLVM <https://llvm.org/docs/BuildingADistribution.html>`_):
   $ cmake -B /path/to/lldb-build -G Ninja \
           -C /path/to/llvm-project/lldb/cmake/caches/Apple-lldb-macOS.cmake \
           -DLLVM_ENABLE_PROJECTS="clang;lldb" \
-          -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi" \
+          -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind" \
           llvm-project/llvm
 
   $ DESTDIR=/path/to/lldb-install ninja -C /path/to/lldb-build check-lldb install-distribution
@@ -386,7 +386,7 @@ Build LLDB standalone for development with Xcode:
   $ cmake -B /path/to/llvm-build -G Ninja \
           -C /path/to/llvm-project/lldb/cmake/caches/Apple-lldb-base.cmake \
           -DLLVM_ENABLE_PROJECTS="clang" \
-          -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi" \
+          -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind" \
           llvm-project/llvm
   $ ninja -C /path/to/llvm-build