Add regression test for rust-lang#100638

Author: GuillaumeGomez

tests/rustdoc/footnote-definition-without-blank-line-100638.rs

@@ -0,0 +1,15 @@
+#![crate_name = "foo"]
+
+//! Reference to footnotes A[^1], B[^2] and C[^3].
+//!
+//! [^1]: Footnote A.
+//! [^2]: Footnote B.
+//! [^3]: Footnote C.
+
+// @has 'foo/index.html'
+// @has - '//*[@class="docblock"]/*[@class="footnotes"]/ol/li[@id="fn1"]/p' 'Footnote A'
+// @has - '//li[@id="fn1"]/p/a/@href' '#fnref1'
+// @has - '//*[@class="docblock"]/*[@class="footnotes"]/ol/li[@id="fn2"]/p' 'Footnote B'
+// @has - '//li[@id="fn2"]/p/a/@href' '#fnref2'
+// @has - '//*[@class="docblock"]/*[@class="footnotes"]/ol/li[@id="fn3"]/p' 'Footnote C'
+// @has - '//li[@id="fn3"]/p/a/@href' '#fnref3'