Bug#57991: Compiler flag change build error : adler32.c

Do not use the same maintainer mode flags for both GCC and ICC.
The -Wall option for ICC enables more warnings than its GCC
counterpart.

config/ac-macros/maintainer.m4

@@ -15,8 +15,11 @@ AC_DEFUN([MY_MAINTAINER_MODE], [
 
 # Set warning options required under maintainer mode.
 AC_DEFUN([MY_MAINTAINER_MODE_WARNINGS], [
+  # Detect ICC posing as GCC.
+  AC_EGREP_CPP([^__INTEL_COMPILER], [__INTEL_COMPILER],
+               [INTEL_COMPILER=no], [INTEL_COMPILER=yes])
   # Setup GCC warning options.
-  AS_IF([test "$GCC" = "yes"], [
+  AS_IF([test "$GCC" = "yes" -a "$INTEL_COMPILER" = "no"], [
     C_WARNINGS="-Wall -Wextra -Wunused -Wwrite-strings -Wno-strict-aliasing -Werror"
     CXX_WARNINGS="${C_WARNINGS} -Wno-unused-parameter"
     C_WARNINGS="${C_WARNINGS} -Wdeclaration-after-statement"