Clarify COMPILER_PLUGINS_CXX_LINKFLAGS vs. COMPILER_PLUGINS_LINKFLAGS

COMPILER_PLUGINS_CXX_LINKFLAGS was introduced with
39e7a72b3e "Support loplugin in clang-cl" to
augment COMPILER_PLUGINS_CXX.  Due to MSVC cl.exe command-line processing,
certain linker-related arguments must come at the very end of the command line,
so cannot be included in COMPILER_PLUGINS_CXX.  COMPILER_PLUGINS_CXX_LINKFLAGS
is specified in autogen.input (along with COMPILER_PLUGINS_CXX) and configure.ac
merely passes it on to its use in compilerplugins/Makefile-clang.mk.

ad5cbcf6ba "try to autodetect flags needed to
build Clang plugins" now needs a configure.ac-internal variable to store the
output of `llvm-config --ldflags ...`, similarly to how
COMPILER_PLUGINS_CXXFLAGS stores the output of `llvm-config --cxxflags`.  It
reused COMPILER_PLUGINS_CXX_LINKFLAGS for that, but that makes it hard for my
clang-cl build to pass my specification of COMPILER_PLUGINS_CXX_LINKFLAGS from
autogen.input to its use in compilerplugins/Makefile-clang.mk.  So rename this
new variable to COMPILER_PLUGINS_LINKFLAGS (matching COMPILER_PLUGINS_CXXFLAGS).

Change-Id: I93b0b50ba94803041773757d9978222e2726f9b0
Reviewed-on: https://gerrit.libreoffice.org/80473
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>
Tested-by: Jenkins

configure.ac

@@ -7014,7 +7014,7 @@ if test "$COM_IS_CLANG" = "TRUE"; then
         AC_PATH_PROG(LLVM_CONFIG, llvm-config,[],$CLANGDIR/bin $PATH)
         if test -n "$LLVM_CONFIG"; then
             COMPILER_PLUGINS_CXXFLAGS=$($LLVM_CONFIG --cxxflags)
-            COMPILER_PLUGINS_CXX_LINKFLAGS=$($LLVM_CONFIG --ldflags --libs --system-libs | tr '\n' ' ')
+            COMPILER_PLUGINS_LINKFLAGS=$($LLVM_CONFIG --ldflags --libs --system-libs | tr '\n' ' ')
             if test -z "$CLANGLIBDIR"; then
                 CLANGLIBDIR=$($LLVM_CONFIG --libdir)
             fi
@@ -7046,14 +7046,14 @@ if test "$COM_IS_CLANG" = "TRUE"; then
             AC_MSG_CHECKING([for clang libraries to use])
             if test -z "$CLANGTOOLLIBS"; then
                 LIBS="-lclangTooling -lclangDriver -lclangFrontend -lclangParse -lclangSema -lclangEdit \
- -lclangAnalysis -lclangAST -lclangLex -lclangSerialization -lclangBasic $COMPILER_PLUGINS_CXX_LINKFLAGS"
+ -lclangAnalysis -lclangAST -lclangLex -lclangSerialization -lclangBasic $COMPILER_PLUGINS_LINKFLAGS"
                 AC_LINK_IFELSE([
                     AC_LANG_PROGRAM([[#include "clang/Basic/SourceLocation.h"]],
                         [[ clang::FullSourceLoc().dump(); ]])
                 ],[CLANGTOOLLIBS="$LIBS"],[])
             fi
             if test -z "$CLANGTOOLLIBS"; then
-                LIBS="-lclang-cpp $COMPILER_PLUGINS_CXX_LINKFLAGS"
+                LIBS="-lclang-cpp $COMPILER_PLUGINS_LINKFLAGS"
                 AC_LINK_IFELSE([
                     AC_LANG_PROGRAM([[#include "clang/Basic/SourceLocation.h"]],
                         [[ clang::FullSourceLoc().dump(); ]])