8339128: Cannot resolve user specified tool properly after JDK-8338304

Reviewed-by: erikj, ihse

make/autoconf/flags-ldflags.m4

@@ -73,7 +73,9 @@ AC_DEFUN([FLAGS_SETUP_LDFLAGS_HELPER],
     if test "x$OPENJDK_TARGET_OS" = xlinux; then
       # Clang needs the lld linker to work correctly
       BASIC_LDFLAGS="-fuse-ld=lld -Wl,--exclude-libs,ALL"
-      UTIL_REQUIRE_PROGS(LLD, lld)
+      if test "x$CXX_IS_USER_SUPPLIED" = xfalse && test "x$CC_IS_USER_SUPPLIED" = xfalse; then
+        UTIL_REQUIRE_PROGS(LLD, lld)
+      fi
     fi
     if test "x$OPENJDK_TARGET_OS" = xaix; then
       BASIC_LDFLAGS="-Wl,-b64 -Wl,-brtl -Wl,-bnorwexec -Wl,-bnolibpath -Wl,-bnoexpall \

make/autoconf/toolchain.m4

@@ -445,6 +445,7 @@ AC_DEFUN([TOOLCHAIN_FIND_COMPILER],
         AC_MSG_ERROR([User supplied compiler $1=[$]$1 does not exist])
       fi
     fi
+    $1_IS_USER_SUPPLIED=true
   else
     # No user supplied value. Locate compiler ourselves.
 
@@ -462,6 +463,7 @@ AC_DEFUN([TOOLCHAIN_FIND_COMPILER],
       HELP_MSG_MISSING_DEPENDENCY([devkit])
       AC_MSG_ERROR([Could not find a $COMPILER_NAME compiler. $HELP_MSG])
     fi
+    $1_IS_USER_SUPPLIED=false
   fi
 
   # Now we have a compiler binary in $1. Make sure it's okay.