Determining if the include file pthread.h exists failed with the following output:
Change Dir: /home/buildroot/autobuild/run/instance-3/output-1/build/fluidsynth-2.1.4/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/make cmTC_98946/fast && make[1]: Entering directory `/home/buildroot/autobuild/run/instance-3/output-1/build/fluidsynth-2.1.4/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_98946.dir/build.make CMakeFiles/cmTC_98946.dir/build
make[2]: Entering directory `/home/buildroot/autobuild/run/instance-3/output-1/build/fluidsynth-2.1.4/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_98946.dir/CheckIncludeFile.c.o
/home/buildroot/autobuild/run/instance-3/output-1/host/bin/arm-none-linux-gnueabi-gcc --sysroot=/home/buildroot/autobuild/run/instance-3/output-1/host/arm-buildroot-linux-gnueabi/sysroot -DTESTKEYWORD=inline  -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -Wall -W -Wpointer-arith -Wcast-qual -Wstrict-prototypes -Wno-unused-parameter -Wdeclaration-after-statement -Werror=implicit-function-declaration -Werror=incompatible-pointer-types -Wbad-function-cast -Wcast-align   -DNDEBUG -fPIE   -o CMakeFiles/cmTC_98946.dir/CheckIncludeFile.c.o   -c /home/buildroot/autobuild/run/instance-3/output-1/build/fluidsynth-2.1.4/CMakeFiles/CMakeTmp/CheckIncludeFile.c
cc1: error: -Werror=incompatible-pointer-types: no option -Wincompatible-pointer-types
make[2]: *** [CMakeFiles/cmTC_98946.dir/CheckIncludeFile.c.o] Error 1
make[2]: Leaving directory `/home/buildroot/autobuild/run/instance-3/output-1/build/fluidsynth-2.1.4/CMakeFiles/CMakeTmp'
make[1]: *** [cmTC_98946/fast] Error 2
make[1]: Leaving directory `/home/buildroot/autobuild/run/instance-3/output-1/build/fluidsynth-2.1.4/CMakeFiles/CMakeTmp'