RFR(XS) 8161915: Linking gtestLauncher may end up linking with non-gtest libjvm

[Mikael Gerdin]

Hi all,

Please review this small fix to work around a problem where incremental 
builds of hotspot would fail due to the symbol runUnitTests missing.

The cause for the problem is that the unit tests launcher linker command 
line contains a -L path containing the standard libjvm.so
  [10] LDFLAGS := -Wl,-z,defs -Wl,-z,now -Wl,-z,relro 
-Wl,--allow-shlib-undefined 
-L/home/mgerdin/work/repos/hg/jdk9/hs-rt-work/build/linux-x64-slowdebug/support/modules_libs/java.base/amd64 
-L/home/mgerdin/work/repos/hg/jdk9/hs-rt-work/build/linux-x64-slowdebug/support/modules_libs/java.base/amd64/server 

  [11] LDFLAGS_unix := 
-L/home/mgerdin/work/repos/hg/jdk9/hs-rt-work/build/linux-x64-slowdebug/hotspot/variant-server/libjvm/gtest 
-Wl,-z,origin -Wl,-rpath,\$$ORIGIN
  [13] LIBS_unix := -ljvm

This is caused by BUILD_GTEST_LAUNCHER picking up LDFLAGS_TESTEXE which 
was recently modified to include -L path to the standard libjvm.so

My suggested fix is to instead use LDFLAGS_JDKEXE for the gtest launcher 
since the only difference between them is that TESTEXE appends 
JAVA_BASE_LDFLAGS:
flags.m4, 687:  LDFLAGS_TESTEXE="$LDFLAGS_JDKEXE $JAVA_BASE_LDFLAGS"

Since the fix is only one line, I'll paste it inline here:
diff --git a/make/lib/CompileGtest.gmk b/make/lib/CompileGtest.gmk
--- a/make/lib/CompileGtest.gmk
+++ b/make/lib/CompileGtest.gmk
@@ -104,7 +104,7 @@
          -I$(GTEST_FRAMEWORK_SRC)/include, \
      CFLAGS_DEBUG_SYMBOLS := $(JVM_CFLAGS_SYMBOLS), \
      CXXFLAGS_DEBUG_SYMBOLS := $(JVM_CFLAGS_SYMBOLS), \
-    LDFLAGS := $(LDFLAGS_TESTEXE), \
+    LDFLAGS := $(LDFLAGS_JDKEXE), \
      LDFLAGS_unix := -L$(JVM_OUTPUTDIR)/gtest $(call 
SET_SHARED_LIBRARY_ORIGIN), \
      LDFLAGS_solaris := -library=stlport4, \
      LIBS_unix := -ljvm, \


Testing: JPRT -testset hotspot
Bug link: https://bugs.openjdk.java.net/browse/JDK-8161915

Please let me know if there is any further testing I should do before 
pushing this.

Thanks
/Mikael