editors/libreoffice: fix build with lld 17 (take 2)

Building editors/libreoffice with lld 17 results in the following link
errors:

  ld: error: version script assignment of 'PRIVATE_1.4' to symbol '_ZN3sal13backtrace_getEm' failed: symbol not defined
  ld: error: version script assignment of 'GLIBCXX_3.4' to symbol '_ZNSs4_Rep20_S_empty_rep_storageE' failed: symbol not defined

Add -Wl,--undefined-version to LDFLAGS to suppress these error, as the
previous fix did not work in all cases.

PR:		274697
Approved by:	office (blanket)
Fixes:		6338934
MFH:		2024Q4

editors/libreoffice/Makefile

@@ -364,6 +364,8 @@ CXXFLAGS_WARN=	-Woverloaded-virtual -Wno-c++11-narrowing \
 CXXFLAGS_WARN=	-Wshadow -Woverloaded-virtual
 .endif
 
+LDFLAGS+=	-Wl,--undefined-version
+
 post-patch:
 .if ${COMPILER_FEATURES:Mlibstdc++}
 	${REINPLACE_CMD} -e 's/gb_CC/gb_CXX/' ${WRKSRC}/solenv/gbuild/platform/unxgcc.mk