Compiled libgcrypt 1.7.8 with bleading edge clang-5 ( 5.0.0 (trunk 305735)) and UBSan on Ubuntu 16.04 x64. Used the following flags:

-O2 -fno-omit-frame-pointer -g -fsanitize=address -fsanitize=undefined -fsanitize=integer -fsanitize-coverage=trace-pc-guard -fno-sanitize-recover=undefined -fsanitize=float-divide-by-zero -fsanitize=float-cast-overflow -fsanitize-undefined-trap-on-error -fno-sanitize-recover=all

Ran the following test:

libgcrypt-1.7.8/tests/keygen
random-csprng.c:1070:16: runtime error: unsigned integer overflow: 0 - 1 cannot be represented in type 'size_t' (aka 'unsigned long')
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior random-csprng.c:1070:16 in