configure: Check CC_STAGE0 for --target support

We previously only checked the stage 1/2 compiler
for --target support. We got away with this for quite a while but it
eventually caught up with us in #21579, where `bytestring`'s new NEON
implementation was unbuildable on Darwin due to Rosetta's seemingly
random logic for determining which executable image to execute. This
lead to a confusing failure to build `bytestring`'s cbits, when `clang`
tried to compile NEON builtins while targetting x86-64.

Fix this by checking CC_STAGE0 for --target support.

Fixes #21579.

configure.ac

@@ -667,8 +667,10 @@ LLVMTarget_CPP=`    echo "$LlvmTarget"`
 AC_SUBST(LLVMTarget_CPP)
 
 dnl ** See whether cc supports --target=<triple> and set
-dnl CONF_CC_OPTS_STAGE[12] accordingly.
-FP_CC_SUPPORTS_TARGET
+dnl CONF_CC_OPTS_STAGE[012] accordingly.
+FP_CC_SUPPORTS_TARGET([$CC_STAGE0], [CONF_CC_OPTS_STAGE0], [CONF_CXX_OPTS_STAGE0], [CONF_GCC_LINKER_OPTS_STAGE0])
+FP_CC_SUPPORTS_TARGET([$CC], [CONF_CC_OPTS_STAGE1], [CONF_CXX_OPTS_STAGE1], [CONF_GCC_LINKER_OPTS_STAGE1])
+FP_CC_SUPPORTS_TARGET([$CC], [CONF_CC_OPTS_STAGE2], [CONF_CXX_OPTS_STAGE2], [CONF_GCC_LINKER_OPTS_STAGE2])
 
 # See rules/distdir-way-opts.mk for details.
 # Flags passed to the C compiler

distrib/configure.ac.in

@@ -201,7 +201,8 @@ AC_SUBST(TargetHasGnuNonexecStack)
 
 dnl ** See whether cc supports --target=<triple> and set
 dnl CONF_CC_OPTS_STAGE[12] accordingly.
-FP_CC_SUPPORTS_TARGET
+FP_CC_SUPPORTS_TARGET([$CC], [CONF_CC_OPTS_STAGE1], [CONF_CXX_OPTS_STAGE1], [CONF_GCC_LINK_OPTS_STAGE1])
+FP_CC_SUPPORTS_TARGET([$CC], [CONF_CC_OPTS_STAGE2], [CONF_CXX_OPTS_STAGE2], [CONF_GCC_LINK_OPTS_STAGE2])
 
 dnl TargetWordSize for settings file
 AC_CHECK_SIZEOF(void *, 4)

m4/fp_cc_supports_target.m4

@@ -6,13 +6,17 @@
 #
 # The primary effect of this is updating CONF_CC_OPTS_STAGE[12] to
 # explicitly ask the compiler to generate code for the $TargetPlatform.
+#
+# $1 = CC
+# $2 = CC_OPTS variable
+# $3 = CXX_OPTS variable
+# $4 = GCC_LINK_OPTS variable
 AC_DEFUN([FP_CC_SUPPORTS_TARGET],
 [
-   AC_REQUIRE([AC_PROG_CC])
    AC_REQUIRE([GHC_LLVM_TARGET_SET_VAR])
-   AC_MSG_CHECKING([whether $1 CC supports --target])
+   AC_MSG_CHECKING([whether $1 supports --target])
    echo 'int main() { return 0; }' > conftest.c
-   if $CC --target=$LlvmTarget -Werror conftest.c > /dev/null 2>&1 ; then
+   if $1 --target=$LlvmTarget -Werror conftest.c > /dev/null 2>&1 ; then
        CONF_CC_SUPPORTS_TARGET=YES
        AC_MSG_RESULT([yes])
    else
@@ -22,12 +26,9 @@ AC_DEFUN([FP_CC_SUPPORTS_TARGET],
    rm -f conftest.c conftest
 
    if test $CONF_CC_SUPPORTS_TARGET = YES ; then
-       CONF_CC_OPTS_STAGE1="--target=$LlvmTarget $CONF_CC_OPTS_STAGE1"
-       CONF_CC_OPTS_STAGE2="--target=$LlvmTarget $CONF_CC_OPTS_STAGE2"
-       CONF_CXX_OPTS_STAGE1="--target=$LlvmTarget $CONF_CXX_OPTS_STAGE1"
-       CONF_CXX_OPTS_STAGE2="--target=$LlvmTarget $CONF_CXX_OPTS_STAGE2"
-       CONF_GCC_LINKER_OPTS_STAGE1="--target=$LlvmTarget $CONF_GCC_LINKER_OPTS_STAGE1"
-       CONF_GCC_LINKER_OPTS_STAGE2="--target=$LlvmTarget $CONF_GCC_LINKER_OPTS_STAGE2"
+       $2="--target=$LlvmTarget $$2"
+       $3="--target=$LlvmTarget $$3"
+       $4="--target=$LlvmTarget $$4"
    fi
 ])