backtrace is required.

This patch is not upstreamable because there is no way to determine if a Linux
build is musl or glibc from qmake.

--- qtdeclarative-opensource-src-5.9.6/src/quick/quick.pro.old	2018-05-30 11:29:13.000000000 +0000
+++ qtdeclarative-opensource-src-5.9.6/src/quick/quick.pro	2018-07-10 00:42:03.150000000 +0000
@@ -16,6 +16,8 @@
     LIBS_PRIVATE += -lgcov
 }
 
+LIBS_PRIVATE += -lexecinfo
+
 QMAKE_DOCS = $$PWD/doc/qtquick.qdocconf
 
 ANDROID_LIB_DEPENDENCIES = \