makefile filter-out

Sure, I can help with that!

The `filter-out` function in a Makefile is used to remove certain strings from a list of strings.

Here's an example of how to use `filter-out` in a Makefile:

# Define a list of files
FILES := file1.txt file2.txt file3.dat file4.pdf

# Remove all files with a .pdf extension
PDF_FILES := $(filter-out %.pdf,$(FILES))

# Print the filtered list of files
all:
    @echo $(PDF_FILES)

In the above example, the `filter-out` function removes all files with a `.pdf` extension from the `FILES` list and stores the resulting list in the `PDF_FILES` variable.

The resulting output when running `make` would be:

file1.txt file2.txt file3.dat

Let me know if you have any further questions!