on clang 12 from Apple's Xcode 12, checking if globals are prefixed by underscore test fails
Imported issue: Initially reported by Dmitrii Pasechnik in https://gforge.inria.fr/tracker/?group_id=135&aid=21856
the reason is that by default the compiler has -Werror on, so no wonder.
How about actually having underscore_test() defined as a C function?
configure:13260: checking if globals are prefixed by underscore
configure:13286: gcc -march=native -g -O3 -fPIC -c conftes1.c >&5 && gcc -march=native -g -O3 -fPIC -c conftes2.s >&5 && gcc -march=native -g -O3 -fPIC -L/Users/dima/software/sagetrac-mirror/local/lib
-Wl,-rpath,/Users/dima/software/sagetrac-mirror/local/lib conftes1.o conftes2.o >&5
conftes1.c:4:1: warning: type specifier missing, defaults to 'int' [-Wimplicit-int]
main () { underscore_test(); }
^
conftes1.c:4:11: error: implicit declaration of function 'underscore_test' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
main () { underscore_test(); }
^
1 warning and 1 error generated.
configure:13289: $? = 1
configure:13286: gcc -march=native -g -O3 -fPIC -c conftes1.c >&5 && gcc -march=native -g -O3 -fPIC -c conftes2.s >&5 && gcc -march=native -g -O3 -fPIC -L/Users/dima/software/sagetrac-mirror/local/lib
-Wl,-rpath,/Users/dima/software/sagetrac-mirror/local/lib conftes1.o conftes2.o >&5
conftes1.c:4:1: warning: type specifier missing, defaults to 'int' [-Wimplicit-int]
main () { underscore_test(); }
^
conftes1.c:4:11: error: implicit declaration of function 'underscore_test' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
main () { underscore_test(); }
^
1 warning and 1 error generated.
configure:13289: $? = 1
configure:13307: error: Test program links neither with nor without underscore.