frost: add example file

This commit adds an example file to demonstrate how to use the module.

Makefile.am

@@ -195,6 +195,17 @@ musig_example_LDFLAGS += -lbcrypt
 endif
 TESTS += musig_example
 endif
+if ENABLE_MODULE_FROST
+noinst_PROGRAMS += frost_example
+frost_example_SOURCES = examples/frost.c
+frost_example_CPPFLAGS = -I$(top_srcdir)/include -DSECP256K1_STATIC
+frost_example_LDADD = libsecp256k1.la
+frost_example_LDFLAGS = -static
+if BUILD_WINDOWS
+frost_example_LDFLAGS += -lbcrypt
+endif
+TESTS += frost_example
+endif
 endif
 
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