The value of the DEBUG variable is append to CXXFLAGS, thereby
overwriting the optimization level set in the CXXFLAGS environment
variable (-Os on alpine by default). Since we prefer to use our
optimization level DEBUG needs to be unset.

diff -upr snapcast-0.15.0.orig/client/Makefile snapcast-0.15.0/client/Makefile
--- snapcast-0.15.0.orig/client/Makefile	2018-10-14 13:27:11.247287578 +0200
+++ snapcast-0.15.0/client/Makefile	2018-10-14 13:27:26.187330181 +0200
@@ -31,7 +31,7 @@ else
 endif
 
 # Simplify building debuggable executables 'make DEBUG=-g STRIP=echo'
-DEBUG=-O3
+DEBUG=
 
 
 CXXFLAGS += $(ADD_CFLAGS) -std=c++0x -Wall -Wno-unused-function $(DEBUG) -DHAS_FLAC -DHAS_OGG -DASIO_STANDALONE -DVERSION=\"$(VERSION)\" -I. -I.. -isystem ../externals/asio/asio/include -I../externals/popl/include -I../externals/aixlog/include -I../externals -I../common
diff -upr snapcast-0.15.0.orig/server/Makefile snapcast-0.15.0/server/Makefile
--- snapcast-0.15.0.orig/server/Makefile	2018-10-14 13:27:11.257287607 +0200
+++ snapcast-0.15.0/server/Makefile	2018-10-14 13:27:18.830642536 +0200
@@ -31,7 +31,7 @@ else
 endif
 
 # Simplify building debuggable executables 'make DEBUG=-g STRIP=echo'
-DEBUG=-O3
+DEBUG=
 
 
 CXXFLAGS += $(ADD_CFLAGS) -std=c++0x -Wall -Wno-unused-function $(DEBUG) -DHAS_FLAC -DHAS_OGG -DHAS_VORBIS -DHAS_VORBIS_ENC -DASIO_STANDALONE -DVERSION=\"$(VERSION)\" -I. -I.. -isystem ../externals/asio/asio/include -I../externals/popl/include -I../externals/aixlog/include -I../externals -I../common