src/temporal/biquad.c: add missing include
src/spectral/filterbank_mel.c: add missing include
examples/utils.h: fix fake debug when no variadic macros
examples/: build with -Wmissing-declarations
src/: build with -Wmissing-declarations
tests/: build with -Wmissing-declarations
examples/: build with -Wdeclaration-after-statement
src/: improve build with -Wdeclaration-after-statement