gcc: Preprocessing directives implementation

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1 4.13 Preprocessing Directives
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11 ⇒Implementation-defined behavior (cpp)Implementation-defined
 behavior, for details of these aspects of implementation-defined
1 behavior.
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1    * 'The locations within '#pragma' directives where header name
1      preprocessing tokens are recognized (C11 6.4, C11 6.4.7).'
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1    * 'How sequences in both forms of header names are mapped to headers
1      or external source file names (C90 6.1.7, C99 and C11 6.4.7).'
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1    * 'Whether the value of a character constant in a constant expression
1      that controls conditional inclusion matches the value of the same
1      character constant in the execution character set (C90 6.8.1, C99
1      and C11 6.10.1).'
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1    * 'Whether the value of a single-character character constant in a
1      constant expression that controls conditional inclusion may have a
1      negative value (C90 6.8.1, C99 and C11 6.10.1).'
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1    * 'The places that are searched for an included '<>' delimited
1      header, and how the places are specified or the header is
1      identified (C90 6.8.2, C99 and C11 6.10.2).'
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1    * 'How the named source file is searched for in an included '""'
1      delimited header (C90 6.8.2, C99 and C11 6.10.2).'
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1    * 'The method by which preprocessing tokens (possibly resulting from
1      macro expansion) in a '#include' directive are combined into a
1      header name (C90 6.8.2, C99 and C11 6.10.2).'
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1    * 'The nesting limit for '#include' processing (C90 6.8.2, C99 and
1      C11 6.10.2).'
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1    * 'Whether the '#' operator inserts a '\' character before the '\'
1      character that begins a universal character name in a character
1      constant or string literal (C99 and C11 6.10.3.2).'
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1    * 'The behavior on each recognized non-'STDC #pragma' directive (C90
1      6.8.6, C99 and C11 6.10.6).'
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1      ⇒Pragmas (cpp)Pragmas, for details of pragmas accepted by GCC
1      on all targets.  ⇒Pragmas Accepted by GCC Pragmas, for
1      details of target-specific pragmas.
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1    * 'The definitions for '__DATE__' and '__TIME__' when respectively,
1      the date and time of translation are not available (C90 6.8.8, C99
1      6.10.8, C11 6.10.8.1).'
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