package/libexecinfo: needs dynamic library

Fix the following build failure raised since the addition of the package
in commit eea8ba446c10701a273432552108d80fb2224ef4:

execinfo.c:32:10: fatal error: dlfcn.h: No such file or directory
   32 | #include <dlfcn.h>
      |          ^~~~~~~~~

Fixes:
 - http://autobuild.buildroot.org/results/ea33c8c6aa5091983837609eec5d129902183ef1

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/libexecinfo/Config.in

@@ -1,7 +1,11 @@
 config BR2_PACKAGE_LIBEXECINFO
 	bool "libexecinfo"
+	depends on !BR2_STATIC_LIBS # dlfcn.h
 	depends on !BR2_TOOLCHAIN_USES_GLIBC
 	help
 	  Library for inspecting program's backtrace
 
 	  https://github.com/mikroskeem/libexecinfo
+
+comment "libexecinfo needs a musl or uclibc toolchain w/ dynamic library"
+	depends on BR2_TOOLCHAIN_USES_GLIBC || BR2_STATIC_LIBS