Remove committed build artifacts from third_party and fix Android FFTW cross-compile

- Untrack all .o and .a files under third_party/ (rnnoise, libspecbleach)
- Add third_party/**/*.o and third_party/**/*.a to .gitignore
- Fix FFTW configure cross-compilation: add $(strip ...) around fftw_host
  macro call and explicit --build flag so configure detects cross-compile
  correctly (GNU make backslash-continuation in define blocks inserts a
  leading space, causing --host= arm-... to be parsed as empty --host)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitignore

@@ -7,6 +7,8 @@ java/build/
 
 # third_party — only fftw is downloaded manually, rnnoise and libspecbleach are tracked
 third_party/fftw/
+third_party/**/*.o
+third_party/**/*.a
 
 # macOS
 .DS_Store

Makefile.android

@@ -238,7 +238,8 @@ $$(ABI_$(1)_FFTW_STAMP): $(FFTW_SRC)/configure
 	@mkdir -p $$(ABI_$(1)_OBJDIR)/fftw-build $$(ABI_$(1)_FFTW_PREFIX)
 	cd $$(ABI_$(1)_OBJDIR)/fftw-build && \
 	  $(abspath $(FFTW_SRC))/configure \
-	    --host=$(call fftw_host,$(1)) \
+	    --build=$(shell uname -m)-linux-gnu \
+	    --host=$(strip $(call fftw_host,$(1))) \
 	    CC="$$(ABI_$(1)_CC)" \
 	    CFLAGS="-fPIC" \
 	    --prefix=$(abspath $$(ABI_$(1)_FFTW_PREFIX)) \
@@ -252,7 +253,8 @@ $$(ABI_$(1)_FFTWF_STAMP): $(FFTW_SRC)/configure
 	@mkdir -p $$(ABI_$(1)_OBJDIR)/fftwf-build $$(ABI_$(1)_FFTWF_PREFIX)
 	cd $$(ABI_$(1)_OBJDIR)/fftwf-build && \
 	  $(abspath $(FFTW_SRC))/configure \
-	    --host=$(call fftw_host,$(1)) \
+	    --build=$(shell uname -m)-linux-gnu \
+	    --host=$(strip $(call fftw_host,$(1))) \
 	    CC="$$(ABI_$(1)_CC)" \
 	    CFLAGS="-fPIC" \
 	    --prefix=$(abspath $$(ABI_$(1)_FFTWF_PREFIX)) \