runtime/StackGap/testme.sh fails to compile in 8u

This is 8u-specific bug, because in original 11u fix (JDK-8197429) the build is handled by the build system itself.

In 8u, however, it fails with:

Compilation flag:
STDERR:
openjdk version "1.8.0-internal-fastdebug"
OpenJDK Runtime Environment (build 1.8.0-internal-fastdebug-shade_2021_04_22_19_10-b00)
OpenJDK 64-Bit Server VM (build 25.71-b00-fastdebug, mixed mode)
/usr/bin/ld: /tmp/ccj5AhI1.o: in function `create_vm':
exestack-gap.c:(.text+0x103): undefined reference to `JNI_CreateJavaVM'
collect2: error: ld returned 1 exit status
/home/shade/trunks/jdk8u-dev/hotspot/test/runtime/StackGap/testme.sh: 72: ./stack-gap: not found