PortAudio: Enable build on macOS/arm64

[ChinYikMing]

Quote from portaudio/config.log:
...
configure:3194: checking whether the C compiler works
configure:3216: gcc -I/opt/homebrew/opt/zlib/include portaudio/lib/.libs/libportaudio.a -framework CoreServices -framework CoreFoundation -framework AudioUnit -framewo rk AudioToolbox -framework CoreAudio -lpthread -lm mini-gdbstub/build/libgdbstub.a conftest.c >&5
clang: error: no such file or directory: 'portaudio/lib/.libs/libportaudio.a'
...
configure:3265: error: C compiler cannot create executables
...

The ./configure script fails on macOS because LDFLAGS includes static libraries (libportaudio.a) that have not yet been built. This causes the compiler check to fail with "C compiler cannot create executables".

This patch unsets LDFLAGS during the configure step to allow the test program to compile and link successfully, enabling builds on macOS.

Related: #76

Environment

OS: macOS/arm64 Version 15.3.1 (Darwin 24.3.0 Darwin Kernel Version 24.3.0)
Compiler: Apple clang version 16.0.0 (clang-1600.0.26.6)

Reproduce

$ make check

Expected error

git submodule update --init portaudio
cd portaudio/ && ./configure --without-sndio
checking build system type... arm-apple-darwin24.3.0
checking host system type... arm-apple-darwin24.3.0
checking target system type... arm-apple-darwin24.3.0
checking for gcc... gcc
checking whether the C compiler works... no
configure: error: in `/tmp/semu/portaudio':
configure: error: C compiler cannot create executables
See `config.log' for more details
make: *** [Makefile:100: portaudio/lib/.libs/libportaudio.a] Error 77

[ChinYikMing]

Tested and also worked on Ubuntu 22.04/x86_64 (6.5.0-41-generic) with gcc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.. @shengwen-tw @Cuda-Chen Could you please verify the claim? Thanks!

[shengwen-tw]

@ChinYikMing

Could you try rewriting like this?

$(PORTAUDIOLIB): export LDFLAGS :=
$(PORTAUDIOLIB): portaudio/Makefile
	cd $(dir $<) && ./configure --without-sndio
	$(MAKE) -C $(dir $<)
...

[Cuda-Chen]

Hi @ChinYikMing ,

It may take more time for me to review as my testing environment encounters an unrecoverable accident.

@shengwen-tw and @jserv , if you and @ChinYikMing thinks no need to test on Linux Kernel 5.15, you can just approve this PR.

[ChinYikMing]

@ChinYikMing

Could you try rewriting like this?

$(PORTAUDIOLIB): export LDFLAGS :=
$(PORTAUDIOLIB): portaudio/Makefile
	cd $(dir $<) && ./configure --without-sndio
	cd $(dir $<) && ./configure --without-sndio
	$(MAKE) -C $(dir $<)
...

cd $(dir $<) && ./configure --without-sndio

@shengwen-tw Is this command redundant? Removing it doesn't affect functionality. It performs the same action as the proposed change, which unsets LDFLAGS. I'll keep the original change for shorter.