populate_sdk_base: Fix grep command usage on old hosts

"man grep" on centos:

-R, -r, --recursive
Read all files under each directory, recursively; this is equivalent to the -d recurse option.

"man grep" on a more recent ubuntu system:

-r, --recursive
Read all files under each directory, recursively, following symbolic links only if they are on the command line. This is equivalent to the -d recurse option.

So we have an issue when the SDK installer (even with buildtools-tarball) is used on old hosts since it may try and dereference paths which it should not. This is caused by differences in the behaviour of grep -r on older systems.

The fix is to wrap this in find so that only real files are found (as elsewhere in the script.

[YOCTO #6577]

index 893afbb..06112dc 100644
@@ -285,7 +285,7 @@ done
 
 # find out all perl scripts in $native_sysroot and modify them replacing the
 # host perl with SDK perl.
-for perl_script in $($SUDO_EXEC grep "^#!.*perl" -rl $native_sysroot); do
+for perl_script in $($SUDO_EXEC find $native_sysroot -type f -exec grep "^#!.*perl" -l '{}' \;); do
 	$SUDO_EXEC sed -i -e "s:^#! */usr/bin/perl.*:#! /usr/bin/env perl:g" -e \
 		"s: /usr/bin/perl: /usr/bin/env perl:g" $perl_script
 done