[Ada] Add/fix documentation for the Double_*_Alignment parameters

2019-08-13  Eric Botcazou  <ebotcazou@adacore.com>

gcc/ada/

	* doc/gnat_ugn/building_executable_programs_with_gnat.rst
	(-gnateT): Document Double_Float_Alignment parameter and fix
	description of Double_Scalar_Alignment parameter.
	* gnat_ugn.texi: Regenerate.

From-SVN: r274337

gcc/ada/ChangeLog

 2019-08-13  Eric Botcazou  <ebotcazou@adacore.com>
 
+	* doc/gnat_ugn/building_executable_programs_with_gnat.rst
+	(-gnateT): Document Double_Float_Alignment parameter and fix
+	description of Double_Scalar_Alignment parameter.
+	* gnat_ugn.texi: Regenerate.
+
+2019-08-13  Eric Botcazou  <ebotcazou@adacore.com>
+
 	* exp_ch6.adb (Expand_Call_Helper): If back-end inlining is
 	enabled, also instantiate the body of a generic unit containing
 	a subprogram subject to aspect/pragma Inline_Always at

gcc/ada/doc/gnat_ugn/building_executable_programs_with_gnat.rst

@@ -1714,11 +1714,13 @@ Alphabetical List of All Switches
   GCC macro ``BITS_PER_WORD`` documented as follows: `Number of bits in a word;
   normally 32.`
 
-  ``Double_Scalar_Alignment`` is the alignment for a scalar whose size is two
-  machine words. It should be the same as the alignment for C ``long_long`` on
-  most targets.
+  ``Double_Float_Alignment``, if not zero, is the maximum alignment that the
+  compiler can choose by default for a 64-bit floating-point type or object.
 
-  ``Maximum_Alignment`` is the maximum alignment that the compiler might choose
+  ``Double_Scalar_Alignment``, if not zero, is the maximum alignment that the
+  compiler can choose by default for a 64-bit or larger scalar type or object.
+
+  ``Maximum_Alignment`` is the maximum alignment that the compiler can choose
   by default for a type or object, which is also the maximum alignment that can
   be specified in GNAT. It is computed for GCC backends as ``BIGGEST_ALIGNMENT
   / BITS_PER_UNIT`` where GCC macro ``BIGGEST_ALIGNMENT`` is documented as

gcc/ada/gnat_ugn.texi

@@ -21,7 +21,7 @@
 
 @copying
 @quotation
-GNAT User's Guide for Native Platforms , Jun 21, 2019
+GNAT User's Guide for Native Platforms , Jul 31, 2019
 
 AdaCore
 
@@ -9452,11 +9452,13 @@ GCC macro @code{BITS_PER_UNIT} documented as follows: @cite{Define this macro to
 @code{Bits_Per_Word} is the number of bits in a machine word, the equivalent of
 GCC macro @code{BITS_PER_WORD} documented as follows: @cite{Number of bits in a word; normally 32.}
 
-@code{Double_Scalar_Alignment} is the alignment for a scalar whose size is two
-machine words. It should be the same as the alignment for C @code{long_long} on
-most targets.
+@code{Double_Float_Alignment}, if not zero, is the maximum alignment that the
+compiler can choose by default for a 64-bit floating-point type or object.
 
-@code{Maximum_Alignment} is the maximum alignment that the compiler might choose
+@code{Double_Scalar_Alignment}, if not zero, is the maximum alignment that the
+compiler can choose by default for a 64-bit or larger scalar type or object.
+
+@code{Maximum_Alignment} is the maximum alignment that the compiler can choose
 by default for a type or object, which is also the maximum alignment that can
 be specified in GNAT. It is computed for GCC backends as @code{BIGGEST_ALIGNMENT
 / BITS_PER_UNIT} where GCC macro @code{BIGGEST_ALIGNMENT} is documented as