https://github.com/cacalabs/libcaca/pull/76

[Modified to just save/restore flags.]

From 07cb730bf3dc49170f0c387d9edcf5537a4e26b6 Mon Sep 17 00:00:00 2001
From: kxxt <rsworktech@outlook.com>
Date: Wed, 21 Jun 2023 00:06:04 +0800
Subject: [PATCH] Disable LTO when checking for fsin/fcos/fldln2/...

LTO might interfere with the instruction detection and produce false positives.
(The conftest.c compiles with `-flto=auto` but fails without it)

The build for riscv64 arch linux fails because of this:
https://archriscv.felixc.at/.status/log.htm?url=logs/libcaca/libcaca-0.99.beta20-2.log

This PR fixes it.
---
 configure.ac | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/configure.ac b/configure.ac
index 27b8d5b4..ee38ead3 100644
--- a/configure.ac
+++ b/configure.ac
@@ -145,6 +145,9 @@ AC_COMPILE_IFELSE(
   AC_DEFINE(HAVE_SLEEP, 1, [Define to 1 if you have the ‘Sleep’ function.])],
  [AC_MSG_RESULT(no)])
 
+OLD_CFLAGS="${CFLAGS}" # Disable LTO when checking for the instructions
+CFLAGS="${CFLAGS} -fno-lto"
+
 AC_MSG_CHECKING(for fsin/fcos)
 AC_COMPILE_IFELSE(
  [AC_LANG_PROGRAM(
@@ -163,6 +166,8 @@ AC_COMPILE_IFELSE(
   AC_DEFINE(HAVE_FLDLN2, 1, [Define to 1 if you have the ‘fldln2’ and other floating point instructions.])],
  [AC_MSG_RESULT(no)])
 
+CFLAGS="${OLD_CFLAGS}"
+
 AC_CHECK_HEADERS(zlib.h)
 AC_CHECK_LIB(z, gzopen, [ZLIB_LIBS="${ZLIB_LIBS} -lz"])