Mark stack as non executable

The linker is unable to detect that executable stack is not required and so marks
libblastrampoline.so as requiring it. Pass `-Wl,-z,noexecstack` to
ensure that the stack is marked as not executable. This improves security and
allows running on systems where SELinux has been configured to disallow
executable stacks.

Author: nalimilan

src/Make.inc

@@ -35,7 +35,8 @@ else
 endif
 
 LBT_CFLAGS := -g -O2 -std=c99 -fPIC -DLIBRARY_EXPORTS -D_GNU_SOURCE $(CFLAGS)
-LBT_LDFLAGS := $(LDFLAGS)
+# Linker doesn't detect automatically executable stack isn't needed
+LBT_LDFLAGS := $(LDFLAGS) -Wl,-z,noexecstack
 
 ifeq ($(OS),Linux)
 # On linux, we need to link `libdl` to get `dlopen`