cmake: disable LTO for some configure checks

Some of zlib-ng's configure tests define a function expecting it to be compiled but
don't call that function, or don't use its return value. This is risky with
LTO where the whole thing may be optimised out, which has happened before:
* https://github.com/zlib-ng/zlib-ng/issues/1616
* https://github.com/zlib-ng/zlib-ng/pull/1622
* https://gitlab.kitware.com/cmake/cmake/-/issues/26103

Closes: https://github.com/zlib-ng/zlib-ng/issues/1841

diff --git a/CMakeLists.txt b/CMakeLists.txt
index b97c202168c91a032ff128fdeae01074161f5e81..f5c86389f2ca98100782fad73fdad54548228afa 100644 (file)
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -301,7 +301,7 @@ if(NOT WITH_RUNTIME_CPU_DETECTION)
         message(STATUS "WARNING: Microsoft Visual Studio does not support compile time detection of CPU features for \"/arch\" before \"AVX\"")
         # Workaround for MSVC. By default MSVC does not define the __SSE*__ macros.
         # Fix it if AVX is enabled.
-        set(CMAKE_REQUIRED_FLAGS "${NATIVEFLAG}")
+        set(CMAKE_REQUIRED_FLAGS "${NATIVEFLAG} ${ZNOLTOFLAG}")
         check_c_source_compiles(
             "#ifndef __AVX__
             #  error \"AVX is not enabled.\"
@@ -491,6 +491,7 @@ endif()
 #
 # Check for __builtin_assume_aligned(x,n) support in the compiler
 #
+set(CMAKE_REQUIRED_FLAGS ${ZNOLTOFLAG})
 check_c_source_compiles(
     "char *test(char *buffer) {
         char *abuffer = __builtin_assume_aligned(buffer,64);
@@ -503,10 +504,12 @@ check_c_source_compiles(
 if(HAVE_BUILTIN_ASSUME_ALIGNED)
     add_definitions(-DHAVE_BUILTIN_ASSUME_ALIGNED)
 endif()
+set(CMAKE_REQUIRED_FLAGS)
 
 #
 # check for __builtin_ctz() support in the compiler
 #
+set(CMAKE_REQUIRED_FLAGS ${ZNOLTOFLAG})
 check_c_source_compiles(
     "int main(void) {
         unsigned int zero = 0;
@@ -519,10 +522,12 @@ check_c_source_compiles(
 if(HAVE_BUILTIN_CTZ)
     add_definitions(-DHAVE_BUILTIN_CTZ)
 endif()
+set(CMAKE_REQUIRED_FLAGS)
 
 #
 # check for __builtin_ctzll() support in the compiler
 #
+set(CMAKE_REQUIRED_FLAGS ${ZNOLTOFLAG})
 check_c_source_compiles(
     "int main(void) {
         unsigned int zero = 0;
@@ -535,6 +540,7 @@ check_c_source_compiles(
 if(HAVE_BUILTIN_CTZLL)
     add_definitions(-DHAVE_BUILTIN_CTZLL)
 endif()
+set(CMAKE_REQUIRED_FLAGS)
 
 #
 # check for ptrdiff_t support