Allow relative paths for ip_sources() and ip_include_directories(), r…

[Risto97]

…elative paths are converted to absolute relative to ${CMAKE_CURRENT_SOURCE_DIR} resolve #93

[Risto97]

Relative paths are now allowed for ip_sources() and ip_include_directories() functions.

Functionality matches the CMake target_sources() functionality:

Changed in version 3.13: Relative source file paths are interpreted as being relative to the current source directory (i.e. CMAKE_CURRENT_SOURCE_DIR). See policy CMP0076.

And `target_include_directories()

Specified include directories may be absolute paths or relative paths. A relative path will be interpreted as relative to the current source directory (i.e. CMAKE_CURRENT_SOURCE_DIR) and converted to an absolute path before storing it in the associated target property. If the path starts with a generator expression, it will always be assumed to be an absolute path (with one exception noted below) and will be used unmodified.

Meaning all relative paths given to target_sources() and target_include_directories() are converted immediately to absolute paths relative to CMAKE_CURRENT_SOURCE_DIR variable.

In short this is now possible

add_ip(test)
target_sources(${IP}
    test1.sv
)