Fix issue where VSCode makefile extension can delete files

The problem is that VSCode's make extension, in order to determine
some information about the project, runs
```
make --dry-run --always-make
```
which despite its name will actually try to remake the configure/*
files. Running `installEpics.pl` on these will delete them first,
then try copy them, resulting in an error.

configure/RULES_BUILD

@@ -532,11 +532,11 @@ endif # LOADABLE_SHRLIB_SUFFIX
 ifneq ($(INSTALL_CONFIGS),)
 $(INSTALL_CONFIG)/%: %
 	$(ECHO) "Installing config file $@"
-	@$(INSTALL) -d -m $(INSTALL_PERMISSIONS) $< $(@D)
+	@$(INSTALL) -d -m $(INSTALL_PERMISSIONS) $(abspath $<) $(abspath $(@D))
 
 $(INSTALL_CONFIG)/%: ../%
 	$(ECHO) "Installing config file $@"
-	@$(INSTALL) -d -m $(INSTALL_PERMISSIONS) $< $(@D)
+	@$(INSTALL) -d -m $(INSTALL_PERMISSIONS) $(abspath $<) $(abspath $(@D))
 endif
 
 $(INSTALL_INCLUDE)/%: $(COMMON_DIR)/%

src/tools/installEpics.pl

@@ -57,6 +57,9 @@
     my $temp   = "$install_dir/TEMP.$name.$$";
     my $target = "$install_dir/$name";
 
+    # Don't try to install the file if it already exists
+    next if $source eq $target;
+
     if (-f $target) {
         next if -M $target < -M $source and -C $target < -C $source;
         # Remove old target, making sure it is deletable first