gdb indirectl tdepends on recent glib, so we have to set
LD_LIBRARY_PATH after gdb has started. This fixes:
```
gdb: symbol lookup error: /lib64/libbabeltrace.so.1: undefined symbol: g_string_free_and_steal
```
Variables by these names are only used from the local wscript and when
running "waf configure", which already for other reasons only can run at
the top-level.
These variables are thus not mandatory and not used.
Done with ad hoc scripting hacks processing unused imports found by pyflakes:
for f in $( find * -name wscript ); do echo; pyflakes $f; done | grep 'waflib.Logs.* but unused' | cut -d: -f1 | while read f; do sed -i 's/^import waflib.Logs as Logs,/import/g' $f; done
for f in $( find * -name wscript ); do echo; pyflakes $f; done | grep 'waflib.Options.* but unused' | cut -d: -f1 | while read f; do sed -i 's/import waflib.Options as Options, /import /g' $f; done
for f in $( find * -name wscript ); do echo; pyflakes $f; done | grep 'waflib.Options.* but unused' | cut -d: -f1 | while read f; do sed -i 's/^from waflib import Options,/from waflib import/g' $f; done
for f in $( find * -name wscript ); do echo; pyflakes $f; done | grep ' imported but unused$' | sed "s/^\([^:]*\):[0-9]*:[0-9]* '\(.*\)'.*/\1 \2/g" | while read f lib; do sed -i "/^import $lib$/d" $f; done
for f in $( find * -name wscript ); do echo; pyflakes $f; done | grep 'waflib.Options.* but unused' | cut -d: -f1 | while read f; do sed -i '/from waflib import Options$/d' $f; done
for f in $( find * -name wscript ); do echo; pyflakes $f; done | grep 'waflib.TaskGen.* but unused' | cut -d: -f1 | while read f; do sed -i '/from waflib import TaskGen$/d' $f; done
for f in $( find * -name wscript ); do echo; pyflakes $f; done | grep 'waflib.Task.Task.* but unused' | cut -d: -f1 | while read f; do sed -i '/^from waflib.Task import Task$/d' $f; done
for f in $( find * -name wscript ); do echo; pyflakes $f; done | grep 'waflib.Tools.winres.* but unused' | cut -d: -f1 | while read f; do sed -i '/^from waflib.Tools import winres$/d' $f; done
for f in $( find * -name wscript ); do echo; pyflakes $f; done | grep 'waflib.Utils.* but unused' | cut -d: -f1 | while read f; do sed -i '/^import waflib.Utils as Utils$/d' $f; done
This fixes a "too many sections" issue
```
Fatal error: can't write 159 bytes to section .text of build/libs/ardour/luabindings.cc.1.o: 'file too big'
x86_64-w64-mingw32-as: build/libs/ardour/luabindings.cc.1.o: too many sections (36781)
```
The old code assumed that the thread that created a request buffer for a given
signal-emitting thread would be the latter thread, and thus a thread-local
pointer to the request buffer could be used. This turns out not to be true: the
GUI thread tends to be responsible for constructing the request buffers for
pre-registered threads.
That mechanism has been replaced by using a RWLock protected map using
pthread_t as the key and the request buffer as the value. This allows any
thread to create and register the request buffers used between any other pair
of threads (because the lookup always uses a pthread_t).
The symptoms of this problem were a signal emitted in an audioengine thread
that was propagated to the target thread, but when the target thread scans its
request buffers for requests, it finds nothing (because it didn't know about
the request buffer). In a sense, the signal was successfully delivered to the
target thread, but no meaningful work (i.e the signal handler) is performed.
