RFR: JDK-8215296 do not disable c99 on Solaris

[Magnus Ihse Bursie]

 From the bug report:
"Currently  we disable C99 in the Solaris build by setting -xc99=%none%.
This differs from a lot of other build environments like gcc/Linux or 
VS2013/2017 on Windows where C99 features work.
We should remove this difference on Solaris and remove or replace the 
setting.

Kim Barrett mentioned :
"I merely mentioned the C++14 work as evidence that removing 
-xc99=%none% didn’t appear harmful."
However it will take more time until  the C++14  change is in."

I am currently running a test build on our CI build system to confirm 
that this does not break the Solaris build (but I'd be highly surprised 
if it did). I will not push this until the builds are cleared.

/Magnus

Bug: https://bugs.openjdk.java.net/browse/JDK-8215296
Patch inline:
diff --git a/make/autoconf/flags-cflags.m4 b/make/autoconf/flags-cflags.m4
--- a/make/autoconf/flags-cflags.m4
+++ b/make/autoconf/flags-cflags.m4
@@ -559,7 +559,7 @@
      TOOLCHAIN_CFLAGS="-errshort=tags"

      TOOLCHAIN_CFLAGS_JDK="-mt $TOOLCHAIN_FLAGS"
-    TOOLCHAIN_CFLAGS_JDK_CONLY="-xc99=%none -xCC -Xa -W0,-noglobal 
$TOOLCHAIN_CFLAGS" # C only
+    TOOLCHAIN_CFLAGS_JDK_CONLY="-std=c99 -xCC -W0,-noglobal 
$TOOLCHAIN_CFLAGS" # C only
      TOOLCHAIN_CFLAGS_JDK_CXXONLY="-features=no%except -norunpath 
-xnolib" # CXX only
      TOOLCHAIN_CFLAGS_JVM="-template=no%extdef -features=no%split_init \
          -library=stlport4 -mt -features=no%except $TOOLCHAIN_FLAGS"