-Wl,-start-group is removed from --libs

[sebhub]

Consider the following name.pc file:

Name: name
Version: 1.0
Description: description
Libs: -Wl,--start-group -la -lb -Wl,--end-group -nodefaultlibs -Wl,--start-group -la -lgcc -Wl,--end-group -Wl,--gc-sections

With pkg-config 1.8.1 I get:

pkg-config --libs name.pc
-lb -Wl,--end-group -nodefaultlibs -Wl,--start-group -la -lgcc -Wl,--end-group -Wl,--gc-sections

This leads to linker errors like this:

ld: group ended before it began (--help for usage)

[kaniini]

This is because the -la fragment is being dropped due to deduplication, which is because the deduplication algorithm is not directly aware of linker groups.

I think two areas of action should be considered here: first, allowing the user to disable the deduplication algorithm entirely, but also to make the deduplication algorithm a little more context-aware.

[kaniini]

(Please also try on latest pkgconf)

[kaniini]

I think to fully fix this I need to change fragments to be stored in a tree rather than as a flattened list. That way we can understand fully the relationships between the fragments, e.g. -Wl,--start-group should have -la, -lb and -Wl,--end-group as child fragments.