depends: Use pic for all linux dependencies

This avoids textrels, and matches previous gitian behavior.

depends/packages/boost.mk

@@ -22,8 +22,7 @@ $(package)_toolset_darwin=darwin
 $(package)_archiver_darwin=$($(package)_libtool)
 $(package)_config_libraries=chrono,filesystem,program_options,system,thread,test
 $(package)_cxxflags=-fvisibility=hidden
-$(package)_cxxflags_x86_64_linux=-fPIC
-$(package)_cxxflags_arm_linux=-fPIC
+$(package)_cxxflags_linux=-fPIC
 endef
 
 define $(package)_preprocess_cmds