Add function like example.

Author: ludgerpaehler

Diff for: 5_fn_like/Makefile

@@ -0,0 +1,10 @@
+all: fn_like.o
+
+clean:
+	rm -f *.o *.ll
+
+%.o: %.c
+	../dockerscript.sh clang-12 /host/$^ -O3 -Xclang -load -Xclang /Enzyme/enzyme/build/Enzyme/ClangEnzyme-12.so -ffast-math -o /host/$@
+
+run-%: %.o
+	../dockerscript.sh /host/$^ 3.14

Diff for: 5_fn_like/fn_like.c

@@ -0,0 +1,24 @@
+#include <stdio.h>
+#include <math.h>
+#include <assert.h>
+
+
+double __enzyme_autodiff(void*, ...);
+
+double log1p_like_function(double a) {
+  return 2*a;
+}
+
+double test(double a) {
+  return log1p_like_function(a);
+}
+
+void* __enzyme_function_like[2] = {(void*)log1p_like_function, "log1p"}; 
+
+int main(int argc, char** argv) {
+
+  double grad_out = __enzyme_autodiff(test, 2.0);
+  printf("Gradient of the log1p like function is %f", grad_out);
+
+  return 0;
+}