Fix Autotools -Werror cleanup (#4144)

The Autotools temporarily scrub -Werror(=whatever) from CFLAGS, etc.
  so configure checks don't trip over warnings generated by configure
  check programs. The sed line originally only scrubbed -Werror but not
  -Werror=something, which would cause errors when the '=something' was
  left behind in CFLAGS.

  The sed line has been updated to handle -Werror=something lines.

  Fixes one issue raised in #3872

configure.ac

@@ -194,12 +194,25 @@ saved_user_LDFLAGS="$LDFLAGS"
 saved_user_CPPFLAGS="$CPPFLAGS"
 
 ## Strip out -Werror from CFLAGS since that can cause checks to fail when
-## compiling the test program fails due to warnings
-CFLAGS="`echo $CFLAGS | sed -e 's/-Werror//g'`"
-CXXFLAGS="`echo $CXXFLAGS | sed -e 's/-Werror//g'`"
-FCFLAGS="`echo $FCFLAGS | sed -e 's/-Werror//g'`"
-JAVACFLAGS="`echo $JAVACFLAGS | sed -e 's/-Werror//g'`"
-CPPFLAGS="`echo $CPPFLAGS | sed -e 's/-Werror//g'`"
+## compiling test programs fails due to warnings
+##
+##  Regex:
+##
+##      -Werror         Literal -Werror
+##      \(              Start optional capturing group
+##      =               Literal equals sign
+##      [^[:space:]-]   Non-space characters
+##      \+              1 or more of the above
+##      \)              End optional capturing group
+##      \?              0 or 1 capturing group matches
+##
+WERROR_SED= "sed -e 's/-Werror\(=[^[:space:]]\+\)\?//g'"
+
+CFLAGS="`echo $CFLAGS | $WERROR_SED`"
+CXXFLAGS="`echo $CXXFLAGS | $WERROR_SED`"
+FCFLAGS="`echo $FCFLAGS | $WERROR_SED`"
+JAVACFLAGS="`echo $JAVACFLAGS | $WERROR_SED`"
+CPPFLAGS="`echo $CPPFLAGS | $WERROR_SED`"
 
 ## Support F9X variable to define Fortran compiler if FC variable is
 ## not used.  This should be deprecated in the future.

release_docs/RELEASE.txt

@@ -575,6 +575,20 @@ Support for new platforms, languages and compilers
 
 Bug Fixes since HDF5-1.14.0 release
 ===================================
+    Configuration:
+    -------------
+    - Fix Autotools -Werror cleanup
+
+      The Autotools temporarily scrub -Werror(=whatever) from CFLAGS, etc.
+      so configure checks don't trip over warnings generated by configure
+      check programs. The sed line originally only scrubbed -Werror but not
+      -Werror=something, which would cause errors when the '=something' was
+      left behind in CFLAGS.
+
+      The sed line has been updated to handle -Werror=something lines.
+
+      Fixes one issue raised in #3872
+
     Library
     -------
     - Fixed asserts raised by large values of H5Pset_est_link_info() parameters