Build fails with LTO

[eli-schwartz]

I tried building with this in *FLAGS: -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing

I got this error:

x86_64-pc-linux-gnu-gcc  -march=native -fstack-protector-all -O2 -pipe -fdiagnostics-color=always -frecord-gcc-switches -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=3 -fstack-clash-protection -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing  -Wformat -Werror=format-security -Werror=implicit-function-declaration -Werror=implicit-int -Werror=int-conversion -Werror=incompatible-pointer-types  -Wl,-O1 -Wl,--as-needed -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing -Wl,--defsym=__gentoo_check_ldflags__=0 -o pngcp pngcp.o pngread.o pngwrite.o inflateraster.o -lpng -lm -lpng -lm 
pngcp.h:4:7: error: type of ‘readimage’ does not match original declaration [-Werror=lto-type-mismatch]
    4 | char *readimage(char *filename, unsigned long *width, unsigned long *height,
      |       ^
pngread.c:10:7: note: ‘readimage’ was previously declared here
   10 | char *readimage(char *filename, png_uint_32 *width, png_uint_32 *height,
      |       ^
pngread.c:10:7: note: code may be misoptimized unless ‘-fno-strict-aliasing’ is used
lto1: some warnings being treated as errors
lto-wrapper: fatal error: x86_64-pc-linux-gnu-gcc returned 1 exit status
compilation terminated.
/usr/lib/gcc/x86_64-pc-linux-gnu/13/../../../../x86_64-pc-linux-gnu/bin/ld: error: lto-wrapper failed
collect2: error: ld returned 1 exit status
make[1]: *** [Makefile:430: pngcp] Error 1

Downstream bug report: https://bugs.gentoo.org/875371
Full build log: build.log