configure: Trust LLVM >= 4.0 llvm-config --libs for shared libraries

No need to manually look for the library files anymore with current
LLVM. This sidesteps the manual method failing when LLVM was built with
-DLLVM_APPEND_VC_REV=ON.

(This might already work with older versions of LLVM)

Acked-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

configure.ac

@@ -2623,11 +2623,12 @@ if test "x$enable_llvm" = xyes; then
     fi
     LLVM_LIBS="`$LLVM_CONFIG --libs ${LLVM_COMPONENTS}`"
 
+    if test "x$enable_llvm_shared_libs" = xyes; then
+        if test $LLVM_VERSION_MAJOR -lt 4; then
             dnl llvm-config may not give the right answer when llvm is a built as a
             dnl single shared library, so we must work the library name out for
             dnl ourselves.
             dnl (See https://llvm.org/bugs/show_bug.cgi?id=6823)
-    if test "x$enable_llvm_shared_libs" = xyes; then
             dnl We can't use $LLVM_VERSION because it has 'svn' stripped out,
             LLVM_SO_NAME=LLVM-`$LLVM_CONFIG --version`
             AS_IF([test -f "$LLVM_LIBDIR/lib$LLVM_SO_NAME.$IMP_LIB_EXT"], [llvm_have_one_so=yes])
@@ -2653,6 +2654,7 @@ if test "x$enable_llvm" = xyes; then
                 dnl install uses a shared object for each component and we have
                 dnl already added all of these objects to LLVM_LIBS.
             fi
+        fi
     else
         AC_MSG_WARN([Building mesa with statically linked LLVM may cause compilation issues])
         dnl We need to link to llvm system libs when using static libs